Low power consumption mis semiconductor device

ABSTRACT

A logic gate is constructed of an insulated gate field effect transistor (MIS transistor) having a thin gate insulation film. An operation power supply line to the logic gate is provided with an MIS transistor having a thick gate insulation film for switching the supply and stop of an operation power source voltage. A voltage of the gate of the power source switching transistor is made changing in an amplitude greater than an amplitude of an input and an output signal to the logic gate. Current consumption in a semiconductor device configured of MIS transistor of a thin gate insulation film can be reduced and an power source voltage thereof can be stabilized.

CROSS REFERENCES AND RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.12/010,427 filed Jan. 24, 2008, which is a Divisional of U.S. patentapplication Ser. No. 11/369,852 filed Mar. 8, 2006 now U.S. Pat. No.7,355,455, which is a Divisional of U.S. patent application Ser. No.10/409,585 filed on Apr. 9, 2003 now U.S. Pat. No. 7,042,245.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to semiconductor devicesincluding an insulated gate field effect transistor (hereinafterreferred to as an MIS transistor) and particularly to configurations forreducing power consumption in semiconductor devices havingmicrofabricated CMOS transistors (p and n channel MIS transistors). Morespecifically, the present invention relates to configurations forreducing gate tunneling current of microfabricated MIS transistors.

2. Description of the Background Art

In CMOS semiconductor devices including CMOS transistors as a component,if an MIS transistor is significantly scaled down in size, an operatingpower supply voltage is reduced in order to ensure the reliability ofthe transistors and to achieve reduced power consumption. When the sizeof MIS transistor is reduced in accordance with the reduction of theoperating power supply voltage, each parameter value of the transistorsis reduced in accordance with a predetermined scaling rule.

According to such scaling rule, the MIS transistor is required to have agate insulation film reduced in thickness, Tox, and a threshold voltage,Vth, reduced in absolute value. However, a threshold voltage cannot bereduced in absolute value in accordance with the scaling rule. Thethreshold voltage is defined as a gate to source voltage causing aprescribed drain current under application of a predetermined drainvoltage.

When the threshold voltage Vth is reduced in absolute value and if agate to source voltage Vgs attains 0V, a weak inversion layer is formedin a channel region and through this inversion layer a subthresholdcurrent hereinafter referred to as an “off-leak current”) flows. Theoff-leak current increases as the threshold voltage decreases inabsolute value. Accordingly, in a standby cycle in which MIS transistoris kept off, the off-leak current increases and a standby currentincreases disadvantageously. In particular, for portable equipment orother battery-driven equipment employing such a semiconductor device,reducing the off-leak current is a significant issue to increase thelifetime of a battery.

When the off-leak current is reduced by increasing the threshold voltageVth in absolute value, an advantage achieved by reduced operating powersupply voltage cannot be insured, and high speed operation cannot beensured. A multi-threshold CMOS (T-CMOS) configuration has beenproposed, for example in Japanese Patent Laying-Open No. 6-29834, toreduce an off-leak current in the standby cycle and also ensure highspeed operation.

In the MT-CMOS configuration proposed in the prior art document, atransistor having a threshold voltage M-Vth with a relatively large(intermediate) absolute value is connected between a main power supplyline and a sub power supply line as a power supply switching transistor.A logic circuit is constructed of L-Vth transistors each having athreshold voltage with a small absolute value. In such logic circuit, atransistor kept off in the standby cycle is connected to the sub powersupply line and a transistor kept conductive in the standby state isconnected to the main power supply line.

In the standby cycle, the power supply switching transistor is kept inthe off state. In the standby cycle, the voltage level of the sub powersupply line is set to be a voltage level making the off-leak current ofthe power supply switching transistor balancing that of the transistorsof the logic circuit. Therefore, due to the voltage drop at the powersupply switching transistor, the transistor connected to the sub powersupply line of the logic circuit has a gate to source voltage reverselybiased to enter a more stronger off state. Thus, the off-leak current isfurther reduced, in conjunction with the small off-leak current of thepower supply switch transistor.

In an active cycle, in which an operation is actually performed, thepower supply switching transistors is set to the on state, the sub powersupply line is connected to the main power supply line. Thus, the logiccircuit, constructed of transistors having a threshold voltage with asmall absolute value, operates at high speed.

Japanese Patent Laying-Open No. 9-116417 discloses that in order to setthe power switching transistors to a stronger off state in the MT-CMOSconfiguration, a high voltage VPP higher than an H level power sourcevoltage VDD is applied to a power switching transistor provided to thepower supply voltage VDD, and a negative voltage VBB is applied to apower switching transistor provided for an L level power source voltageVSS.

Various parameters of an MIS transistor, such as feature size, arescaled down in accordance with a scaling rule. Such scaling rule standson the premise that the gate length and the thickness of the gateinsulation film of the MIS transistor are scaled down in accordance witha common shrinking rate. For example, an MIS transistor having a gatelength of 0.25 μm has a gate insulation film generally having athickness of 5 nm. Accordingly, an MIS transistor having a gate lengthof the order of 0.1 μM has a gate insulation film having a thickness ofthe range of 2.0 to 2.5 nm.

If a gate insulation film is reduced in thickness as an operating powersupply voltage is reduced, e.g., the gate insulation film is reduced tosubstantially 3 nm under the condition of a power supply voltage of nomore than 1.5V, a tunneling current flows through the gate insulationfilm of the MIS transistor in the on state (conductive state) and apower source current through the transistor in the on state increasesdisadvantageously.

Japanese Patent Laying-Open No. 11-150193 discloses that such a gatetunneling leak current might be reduced by a control circuit constructedof an MIS transistor of a thick gate insulation film and controllingturning on/off of the power switching transistor.

FIGS. 30A to 30C schematically show an energy band of an MIS structure.FIGS. 30A to 30C show, as an exemplary energy band, a band for astructure with a gate formed of a metal. Typically, in an MIS structure,a gate is formed of polysilicon doped with an impurity and has aproperty of semiconductor. However, to simplify the description, thegate is assumed to be formed of metal. In addition, the semiconductorsubstrate region is a p type substrate.

As shown in FIG. 30A, if the gate receives a negative voltage V, holespresent in the p type substrate are attracted to an interface with theinsulation film and the energy band of the p type substrate bends, atthe interface between the insulation film and the p substrate, upwardand a valence band Ev approaches a Fermi level EF. Furthermore, aconduction band Ec also bends upward in a vicinity of this interface.

When the negative voltage is applied, the Fermi level EF of the gate(corresponding to conduction band Ec for a polysilicon gate) alsoincreases. In this condition, in the p type substrate, the density ofmajority carriers (holes) is increased at the interface, as comparedwith an inside thereof, and such state is referred to as an accumulatedstate. In this state, the conduction band Ec bends upward and a barrieragainst electrons is increased in height, and no current tunnels throughthe gate insulation film.

As shown in FIG. 30B, when the gate receives a low positive voltage V,the Fermi level EF (valence band Ec) of the gate decreases andresponsively the p type substrate region also has the conduction band Ecand the valence band Ev banding downward at its interface with theinsulation film. Holes are moved away from the interface with theinsulation film, to cause the poor state of majority carriers (holes).Fermi level EF at the interface is positioned substantially at thecenter of a forbidden band and no majority carrier is present, and sucha state is referred to as a “depletion state.” In the depletion state,no carrier is present at an interface and, similarly, a tunnelingcurrent is not generated.

As shown in FIG. 30C, when the gate receives a larger positive voltageV, the Fermi level EF at the gate is further reduced and in the p typesubstrate, the band bending further increased in a vicinity of theinterface. Consequently, in the vicinity of the interface of the p typesubstrate, Fermi level EF is increased to be higher than an intermediatevalue Eg/2 of an energy gap Eg and minority carriers, or electrons, arestored. Since the interface is opposite in conductivity to an inside,this state is referred to as an “inverted state.”

This inverted state corresponds to a state of a channel being formed inan MIS transistor, and if the gate insulation film has a thickness 5,for example, of 3 nm, the minority carriers, or electrons, cause thetunneling phenomenon and flows to the gate. In other words, in an MIStransistor with a channel being formed, i.e., an MIS transistor in theon state, a tunneling current flows from a channel region to the gatedirectly. This tunneling current is referred to as a (direct) gatetunnel current.

This issue of disadvantageous gate tunnel current similarly applied toan n type substrate region, with the modification that the gate receivesa voltage opposite in polarity and the energy band bends in the oppositedirections.

As described above, if an MIS transistor has a gate insulation filmreduced in thickness to 3 nm, for example, a gate tunnel currentdirectly flows from the channel region to the gate. This gate tunnelcurrent becomes the same in magnitude as an off-leak current when thegate insulation film has a thickness of the order of 3 nm. When the gateinsulation film is reduced in thickness below 3 nm, the gate tunnelcurrent increases to be greater in magnitude than the off-leak current.Thus, if an operating power supply voltage is decreased and a gateinsulation film is reduced in thickness in accordance with a scalingrule, this gate tunnel current attains an insignificant, significantvalue and accordingly, a current consumed in the standby cycleincreases.

A gate tunnel current J satisfies a relationship approximatelyrepresented by the following expression:

J˜E·exp[−Tox·A·√{square root over (φ)}],

where φ represents a height of a barrier of an interface of the gateinsulation film and approximately represented by a difference between asurface potential φs of the interface and Fermi level, A represents aconstant determined by a concentration of an impurity (an effective massof an electron) of a semiconductor substrate of a channel region, and Erepresents an electric field applied across the gate insulation film.

The barrier height φ is a function of a dielectric constant ∈i of thegate insulation film and thickness Tox of the gate insulation film. Forexample, if silicon oxide film is used to form the gate insulation filmand the tunnel current flows at the thickness of 3 nm, such a gatetunnel current is also caused to flow in a gate insulation filmproviding the same barrier height as the silicon oxide film of 3 nmthickness. The gate insulation film can be formed of silicon oxinitridefilm, other than silicon oxide film.

If such a microfabricated MIS transistor is included as a component, thegate tunnel current of MIS transistor attains to be same as or greaterin amount than an off-leak current in the standby state and a currentconsumed in the standby cycle cannot be reduced.

FIG. 31 shows a configuration of the MT-CMOS circuit disclosed inJapanese Patent Laying-Open No. 11-150193. In FIG. 31, a logic circuitis constructed of CMOS inverters IVa and IVb cascaded in two stages, byway of example. CMOS inverters IVa and IVb each include a p channel MIStransistor QPT having a source connected to a sub power supply line SPLand an n channel MIS transistor QNT having a source connected commonlyto a sub ground line SGL. MIS transistors QPT and QNT in inverters IVaand IVb are each made to have a gate insulation film less than 2.5 nm inthickness.

Sub power supply line SPL is connected to a main power supply line MPLvia a power supply switching transistor PS, and sub ground line SGL isconnected to a main ground line MGL via a power supply switchingtransistor NS. Power supply switching transistor NS has its gatereceiving a switch control signal SWCT, and power supply switchingtransistor PS has its gate receiving switch control signal SWCT via aCMOS inverter CIV. CMOS inverter CIV includes p and n channel MIStransistors each having a gate insulation film set to be not smallerthan 4 nm in thickness. CMOS inverter CIV receives a power supplyvoltage VCC on main power supply line MPL and a ground voltage on mainground line MGL as operating power supply voltages. In other words, inCMOS inverter CIV, the p channel MIS transistor has its source connectedto main power supply line MPL, and the channel MIS transistor has itssource connected to main ground line MGL.

Power supply switching transistors PS and NS have their gate insulationfilms set to be not smaller than 2.5 nm in thickness.

In the configuration of FIG. 31, in a standby state, switch controlsignal SW attains an L level (logical low level), and CMOS inverter CIVoutputs a signal of an H level (logical high level). Responsively, powersupply switching transistors NS and PS both turn off. Sub power supplyline FPL and sub ground line SCL are each set to a floating state, andthe output states of inverters IVa and IVb become unstable.

The voltage levels of sub power supply line SPL and sub ground line SGLin the standby state are determined by a leak current of the logiccircuit. Transistor parameters vary within a permissible range for eachchip, the voltage levels of the sub power supply and ground lines cannotbe maintained at predetermined voltage levels. Accordingly, the subground and power supply lines are different in voltage for differentchips, and inverters IVa and IVb, when transitioning to an active cycle,are different in output voltage level. Thus, it is necessary todetermine a circuit operation timing with a worst case considered, andhigh speed and stable operation cannot be achieved.

Furthermore, in Japanese Patent Laying-Open No. 11-150193, in order toreduce the gate leak current in inverters IVa and IVb, well regions ofMIS transistors QPT and QNT are isolated from each other. This resultsin a disadvantageously increased layout area in the case of an increasednumber of stages of inverters IVa and IVb.

Moreover, gate to source voltage Vgs of each of power supply switchingtransistors PS and NS in a conductive state is the power supply voltageVCC level. If power supply voltage VCC is set to an L level, powersupply switching transistors PS and NS cannot enter a sufficiently deepon state and, in the active cycle, sub power supply and ground lines SPLand SGL cannot be held stably at prescribed power supply and groundvoltage levels, respectively. In particular, if power supply noise isgenerated, the noise cannot be absorbed rapidly, a circuit cannot beoperated stably, and the noise reduces a circuit operating margin.

Furthermore, if driving ability of the power supply switching transistorcannot be increased sufficiently, the sub power supply and ground linescannot be driven rapidly to prescribed voltage levels in transition fromthe off state to an on state. Consequently, a certain period of time isrequired before an operation starts, which is an obstacle against highspeed operation.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a semiconductordevice capable of reducing a current dissipation in a standby state witha simple circuit configuration.

It is another object of the present invention to provide a semiconductordevice capable of more reliably reducing a current consumed in a standbystate and of achieving a high speed operation in transition to an activecycle.

A semiconductor device according to a first aspect of the presentinvention includes: a logic gate constructed of an insulated gate fieldeffect transistor having a first gate insulation film, and receiving avoltage of an internal power node as an operating power source voltageto operate, for processing a signal having a first amplitude; and afirst switching transistor connected between the internal power node anda first power source node, having a second gate insulation film greaterin thickness than the first gate insulation film, and responsive to aswitch control signal of a second amplitude greater than the firstamplitude for selectively rendered conductive to electrically couple thefirst power source node and the internal power node together.

A semiconductor device according to a second aspect of the presentinvention includes: a logic gate constructed of an insulated gate fieldeffect transistor having a first gate insulation film, and receiving avoltage of an internal power node as an operating power supply voltageto operate, for processing a received signal; a first switchingtransistor connected between the internal power node and a first powersource node, having a second gate insulation film greater in thicknessthan the first gate insulation film, and responsive to a switch controlsignal to be selectively rendered conductive, for electrically couplingthe first power source node and the internal power node together; and aswitch circuit for switching an amplitude of the switch control signalin response to an amplitude control signal.

A semiconductor device according to an third aspect of the presentinvention includes: a logic gate including, as a component, an insulatedgate field effect transistor having a first gate insulating film,receiving a voltage of a internal power node as an operating powersupply voltage to process a received signal; a first switchingtransistor connected between the internal power node and a first powersource node, having a gate insulation film greater in thickness than thefirst gate insulation film, responsive to a switch control signal to beselectively made conductive for electrically coupling the first powersource node and the internal power node together; and a prechargecircuit selectively enabled in response to an operation mode instructionsignal instructing a mode of operation of the logic gate to prechargethe internal power node to a prescribed voltage level.

According to the arrangements as described above, a power source linecan be reinforced in an active cycle and a logic circuit can quickly beoperated and the power supply switching transistor can be reliably keptin an off state to reduce a leak current during a standby state.

The foregoing and other objects, features, aspects and advantages of thepresent invention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a configuration of a semiconductor device according to afirst embodiment of the present invention;

FIG. 2 is timing chart representing an operation of the semiconductordevice shown in FIG. 1;

FIG. 3 schematically shows a configuration of a power supply of thesemiconductor device according to the present invention in the firstembodiment;

FIG. 4 schematically shows a configuration of a modification of thepower supply of the semiconductor device in the first embodimentaccording to the present invention;

FIG. 5 shows a further configuration of the power supply of thesemiconductor device according in the first embodiment of the presentinvention;

FIG. 6 shows a modification of the first embodiment according to thepresent invention;

FIG. 7 is timing chart representing an operation of the semiconductordevice shown in FIG. 6;

FIG. 8 shows a configuration of the semiconductor device according tothe present invention in a second embodiment;

FIG. 9 shows a modification of the second embodiment according to thepresent invention;

FIG. 10 shows a configuration of the semiconductor device according tothe present invention in a third embodiment;

FIG. 11 shows a modification of the third embodiment according to thepresent invention;

FIG. 12 shows another exemplary modification of the third embodimentaccording to the present invention;

FIG. 13 shows a configuration of the semiconductor device according to afourth embodiment of the present invention;

FIG. 14 is timing chart representing an operation of the semiconductordevice shown in FIG. 13;

FIG. 15 shows a configuration of a portion generating a switch controlsignal shown in FIG. 13;

FIG. 16 shows a configuration of a modification of the fourth embodimentaccording to the present invention;

FIG. 17 is timing chart representing an operation of the semiconductordevice shown in FIG. 16;

FIG. 18 shows a configuration of a second modification of the fourthembodiment according to the present invention;

FIG. 19 is timing chart representing an operation of the semiconductordevice shown in FIG. 18;

FIG. 20 shows a configuration of a portion generating a switch controlsignal shown in FIG. 18;

FIG. 21 shows a configuration of the semiconductor device according to afifth embodiment of the present invention;

FIG. 22 is timing chart representing an operation of the semiconductordevice shown in FIG. 21;

FIG. 23 shows a configuration of the semiconductor device according to asixth embodiment of the present invention;

FIG. 24 is timing chart representing an operation of the semiconductordevice shown in FIG. 23;

FIG. 25 shows a configuration of the semiconductor device according to aseventh embodiment of the present invention;

FIG. 26 is timing chart representing an operation of the semiconductordevice shown in FIG. 25;

FIG. 27 shows an example of a configuration generating a control signalshown in FIG. 25;

FIG. 28 shows a configuration of the semiconductor device according toan eighth embodiment of the present invention;

FIG. 29 is timing chart representing an operation of the semiconductordevice shown in FIG. 28;

FIGS. 30A to 30C illustrate an energy band of an MIS capacitor; and

FIG. 31 shows a configuration of a conventional semiconductor device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

FIG. 1 shows a configuration of a semiconductor device according to thepresent invention in a first embodiment. In FIG. 1, the semiconductordevice includes, as an internal function circuit, CMOS inverters IV1 toIV4 cascaded in four stages by way of example. CMOS inverters IV1 to IV4each include a p channel MIS transistor PT and an n channel MIStransistor NT. MIS transistors PT and NT each have a gate insulationfilm having a thickness Tox1, for example, of 2 nm.

The p channel MIS transistors of CMOS inverters IV1 to IV4 have theirrespective sources and substrate regions (or backgates) connectedcommonly to a high-side virtual power source line (hereinafter simplyreferred to as a virtual power supply line) VCCV. The n channel MIStransistors of CMOS inverters IV1 to IV4 have their respective sourcesand substrate regions connected commonly to a low-side virtual powersource line (hereinafter simply referred to as a virtual ground line)GNDV.

Virtual power supply line VCCV is coupled with a power supply node via aswitching transistor SW1, and virtual ground line GNDV is connected to aground node via a switching transistor SW2.

Switching transistor SW1 is comprised of a p channel MIS transistorhaving a gate insulation film with a thickness Tox2. P channel MIStransistor PQ has its source and backgate connected to a power supplynode supplying a power supply voltage Vcc1, for example, of 1.0V.

Switching transistor SW2 is comprised of an n channel MIS transistorhaving a gate insulation film with thickness Tox2. N channel MIStransistor NQ has its source and backgate connected to a ground node.Thickness Tox2 of the gate insulation film is, for example, 5.5 nm.

Switching transistor SW1 receives a switch control signal /φ from a CMOSinverter CTL at a gate thereof, and switching transistor SW2 receives aswitch control signal φ at a gate thereof.

CMOS inverter CTL receives a power supply voltage Vcc2 and a groundvoltage as operating power supply voltages. Power supply voltage Vcc2is, for example, 2.5V, which is higher than power supply voltage Vcc1.CMOS inverter CTL is similar in configuration to CMOS inverters IV1 toIV4 shown in FIG. 1 and its constituent p- and n-channel MIS transistorseach have a gate insulation film with thickness Tox2.

Inverter IV1 at an initial input stage of CMOS inverters IV1 and IV4,receives an input signal S. Input signal S has an amplitudecorresponding to power supply voltage Vcc1. Switch control signals φ and/φ are control signals having an amplitude Vcc2 larger than the voltageVcc1, and they are set to an L level or an H level depending on a modeof operation of CMOS inverters IV1 to IV4.

FIG. 2 is timing chart representing an operation of the semiconductordevice shown in FIG. 1. With reference to FIG. 2, an operation of thesemiconductor device shown in FIG. 1 will now be described.

When this semiconductor device is in a standby state, input signal S isin an indefinite state. In the standby state, switch control signal φ isat the ground voltage GND level and complementary switch control signal/φ output from CMOS inverter CTL is at the level of the voltage Vcc2.

In power supply switch circuit SW1, MIS transistor PQ receives thevoltage Vcc2 at the gate and the voltage Vcc1 at the source, and itsgate to source voltage becomes a deep, reverse bias state. Accordingly,an of f leak current can further be reduced in MIS transistor PQ, and aleak current flowing to virtual power supply line VCCV from a powersupply node through power switch circuit SW1 can be suppressedsufficiently. In addition, power supply switch circuit SW2 also has itsIS transistor NQ made non-conductive in the standby state.

If a gate tunnel current flows in CMOS inverters IV1 to IV4 and thevoltage level of virtual ground line GNDV increases, a voltage ascent onthe virtual ground line GNDV is caused by a supply of a current fromvirtual power supply line VCCV. Therefore, the voltage level of thevirtual power supply line VCCV accordingly decreases, the gate potentialof the MIS transistor causing a gate tunnel current flow variesaccordingly, the MIS transistor in the on state is driven substantiallyto the off state, to cut off a path of the gate tunnel current flow.

In this state, CMOS inverters IV1 to IV4 each enter substantially anoutput high impedance state. The voltage level of virtual power supplyline VCCV and virtual ground line GNDV are set to the level, at which aleak current flowing through power supply switch circuits SW1 and SW2balances a leak current flowing through inverters IV1 to IV4.

When an active cycle starts and an operation on the input signal S isperformed, switch control signal φ rises to the level of the voltageVcc2, while complementary switch control signal /φ output from CMOSinverter CTL falls to a ground voltage level. Responsively, in powersupply switch circuits SW1 and SW2, MIS transistors PQ and NQ turnconductive, virtual power supply line VCCV is coupled with a powersupply node, and virtual ground line GNDV is connected to a ground node.

Switch control signal φ is at the level of the voltage Vcc2, which ishigher than the voltage Vcc1. In power supply switch circuit SW2, MIStransistor NQ enter a deeper on state to reliable fix the voltage ofvirtual ground line GNDV to the ground voltage level. Accordingly, thevoltage level of virtual ground line GNDV can be rapidly stabilized anda noise generated in operation on the virtual ground line can bereliably absorbed. Even if MIS transistor NQ has a gate insulation filmas thick as Tox2, stable ground voltage GND can be supplied to virtualground line GNDV and CMOS inverters IV1 to IV4 can be operated stably.

Even if CMOS inverters IV1 to IV4 are configured to use an MIStransistor having a gate insulation film with thickness Tox, forexample, of 2.0 nm, they can be operated stably at high speed in theactive cycle.

FIG. 3 shows an example of a configuration of a portion for generatingpower supply voltages Vcc1 and Vcc2. In FIG. 3, the semiconductor deviceincludes an internal circuit 1 and an I/O interface circuit 2 allowingtransmission of signal/data between the internal circuit 1 and anexternal device or unit. Internal circuit 1 includes an internalfunction circuit 6 containing CMOS inverters IV1 to IV4 and power supplyswitch circuits SW1 and SW2 shown in FIG. 1, and a control circuit 5 forgenerating switch control signals φ and /φ controlling a power supply ofinternal function circuit 6.

Signal/data is transferred between internal function circuit 6 and I/Ointerface circuit 2. Control circuit 5 may receive an operation modeinstruction signal via I/O interface circuit 2 to generate switchcontrol signals φ and /φ in response to the operation mode instructionsignal (instructing a mode of operation of internal function circuit 6).

Power supply voltage Vcc1 is generated in accordance with an externalpower supply voltage EXVcc1 applied externally via a power supply node3, and power supply voltage Vcc2 is generated from a power supplyvoltage EXVcc2 applied externally via a power supply node 4. Therefore,power supply voltages Vcc1 and Vcc2 have their voltage levels determinedby external power supply voltages EXVcc1 and EXVcc2. Power supplyvoltage Vcc2 is supplied to I/O interface circuit 2 and control circuit5, and power supply voltage Vcc1 is supplied to internal functioncircuit 6.

Via an external ground node 7, a ground voltage EXGND is supplied, andan internal ground voltage GND is produced. Ground voltage GND may besupplied to I/O interface circuit 2 and to internal function circuit 6separately. I/O interface circuit 2 receives ground voltage GND througha terminal (node) and internal function circuit 6 and control circuit 5receive ground voltage GND through a separate another terminal (ornode), in order to prevent an operation of I/O interface circuit 2inputting and outputting a signal/data from adversely affecting anoperation of internally provided control circuit 5 and internal functioncircuit 6.

The two kinds of power supply voltages EXVcc1 and EXVcc2 are externallyapplied as shown in FIG. 3, and thus, internal power supply voltagesVcc1 and Vcc2 can be readily produced without necessity of providing aparticular, internal voltage generation circuit.

FIG. 4 shows another configuration of the portion for generating powersupply voltages Vcc1 and Vcc2. In FIG. 4, internal power supply voltageVcc1 is generated from an external power supply voltage EXVcc appliedexternally through power supply node 3. Power supply voltage Vcc2 isgenerated by a boost circuit 10 for boosting power supply voltage Vcc1.Power supply voltage Vcc1 is supplied to logic circuit 6 and powersupply voltage Vcc2 from boost circuit 10 is supplied to control circuit5. Control circuit 5 outputs switch control signals φ and /φ applied toa power supply switch circuit included in internal function circuit 6.Internal function circuit 6 includes the CMOS inverter and the powersupply switch circuit as shown in FIG. 1.

Through a ground node 7, ground voltage EXGND is supplied and internalground voltage GND is generated.

In the power supply configuration shown in FIG. 4, power supply voltagesVcc1 and Vcc2 are produced from external power supply voltage EXVcc1. Inparticular, by generating the power supply voltage vcc2 through the useof boost circuit 10, power supply voltage Vcc2 at a desired voltagelevel can be generated. Generating power supply voltage Vcc2 in boostcircuit 10 provided internal to the semiconductor device can eliminatethe necessity of externally, constantly supplying a voltagecorresponding to power supply voltage Vcc2, and alleviate a requirementon a power supply of a system to which the semiconductor device isapplied. Boost circuit 10 is constructed, for example, by a charge pumpcircuit utilizing a charge pumping operation of a capacitor.

Using boost circuit 10 to generate power supply voltage Vcc2 allowsgeneration of power supply voltage Vcc2 at an optimal voltage level.Thus, in the standby, an MIS transistor at a high-side power sourceswitch circuit is set to a deeper off state, to reduce an off leakcurrent, and in an active operation, an MIS transistor at a low-sidepower source switch circuit can be set to a deeper on state, animpedance of the ground line can be reduced to stabilize a groundvoltage.

FIG. 5 schematically shows a further configuration of the circuit forgenerating power supply voltages Vcc1 and Vcc2. In the arrangement ofFIG. 5, internal power supply voltage Vcc2 is generated from externalpower supply voltage EXVcc2 supplied from a power supply node 4 and issupplied to control circuit 5 as an operating power supply voltage. Adown converting circuit 12 down-converts internal power supply voltageVcc2 to generate power supply voltage Vcc1. Internal function circuit 6is supplied from down converting circuit 12 with power supply voltageVcc1. Control circuit 5 generates switch control signals φ and /φ of anamplitude of Vcc2, as in the arrangement described in the arrangementshown in FIGS. 3 and 4.

Ground voltage GND is generated in accordance with external groundvoltage EXGND supplied to ground node 7 and is supplied to controlcircuit 5 and internal function circuit 6.

With down-converting circuit 12 to generate power supply voltage Vcc1 tointernal function circuit 6, if external power supply voltage EXVcc2 canbe used as a system power supply, power supply voltage Vcc1 can begenerated at a desired voltage level to be supplied to internal functioncircuit 6. Power supply voltage Vcc1 can be set to an optimal levelaccommodating for an operation condition of internal function circuit 6.

First Modification

FIG. 6 shows a configuration of the semiconductor device of a firstmodification of the first embodiment. In the configuration of FIG. 6, incontrol circuit 5 generating switch control signals φ and /φ, there areprovided an inversion circuit CTL1 having a level conversion functionand receiving a mode instructing signal φFB, and a CMOS inverter CTL2receiving a signal from inversion circuit CTL1 to generate switchcontrol signal /φ.

Inversion circuit CTL1 and CMOS inverter CTL2 receive power supplyvoltage Vcc2 and a negative voltage VBB as operating power supplyvoltages. Therefore, switch control signals φ and /φ changes between thevoltage Vcc2 and negative voltage VBB.

Negative voltage VBB is generated from a VBB generation circuit 15receiving power supply voltage Vcc2 to generate negative voltage VBBthrough, for example, a charge pumping operation. Power supply voltageVcc2 is generated from external power supply voltage EXVcc2 supplied topower supply node 2.

Internal function circuit 6 shown in FIG. 6 has the same configurationas that shown in FIG. 1. Accordingly, like components are denoted bylike reference characters and detailed description thereof will not berepeated.

FIG. 7 is timing chart representing an operation of the semiconductordevice shown in FIG. 6. With reference to FIG. 7, the operation of theFIG. 6 semiconductor device will now be described.

VBB generation circuit 15 generates negative voltage VBB from powersupply voltage Vcc2. In a standby cycle, mode instructing signal φFB isat the H level and inversion circuit CTL1 with the level conversionfunction outputs switch control signal φ at a negative voltage VBBlevel. CMOS inverter CTL2 outputs switch control signal /φ at a level ofpower supply voltage Vcc2. In power supply switch circuit SW2, MIStransistor NQ receives negative voltage VBB at a gate thereof and entersa deep reverse bias state between the gate and the source, tosufficiently suppress an off leak current. In power supply switchcircuit SW1, MIS transistor PQ receives power supply voltage Vcc2 higherthan the source voltage Vcc1 at the gate, to be in a deep off state.Therefore, in the standby cycle, an off leak current in power supplyswitch circuits SW1 and SW2 can reliably be reduced. Accordingly, a gatetunnel current and an off leak current can be reduced in CMOS invertersIV1 to IV4 to reduce a current consumption in the standby cycle.

In the active cycle, mode instructing signal φFB attains the L level,and inversion circuit CTL1 with the level conversion function outputsswitch control signal φ at the power supply voltage Vcc2 level and CMOSinverter CTL2 outputs switch control signal /φ of the negative voltageVBB level. Thus, in power supply switch circuits SW1 and SW2, MIStransistors PQ and NQ enter a deep on state, and virtual power supplyline VCCV and virtual ground line GNDV are reliably fixed at the powersupply voltage Vcc1 level and the ground voltage GND level,respectively. CMOS inverters IV1-1V4 accordingly operate stably.

Furthermore, when the standby cycle transitions to the active cycle, thevoltage levels of virtual power supply line VCCV and virtual ground lineGNDV can quickly be stabilized, to operate a logic circuit at highspeed.

Note that power supply voltage Vcc1 may be generated by down-convertingpower supply voltage Vcc2 or may be supplied externally.

As described above, in accordance with the first embodiment of thepresent invention, a control signal of a power supply switch transistorbetween a virtual power source line and a power source node is madelarger in amplitude than an input signal of a logic circuit receiving avoltage of the virtual power source line as an operating power sourcevoltage. Thus, in a standby state, a power supply switch circuit can beset to a deeper off state, a leak current can be reduced in the standby.Furthermore, in an active cycle, the power supply switch circuit can beset to a deep on state, the virtual power source line can reliably befixed at a prescribed voltage level, power source noise can be reduced,and a logic circuit can operate stably.

Herein, the virtual power source line generally refers to a virtualpower supply line and a virtual ground line and corresponds to a firstpower supply node. A power source node corresponds to an internal powernode.

Second Embodiment

FIG. 8 shows a configuration of the semiconductor device according to asecond embodiment of the present invention. The semiconductor deviceshown in FIG. 8 includes, in addition to the configuration of thesemiconductor device shown in FIG. 1, a power supply switch circuit SW3provided between a virtual power supply line VCCV and a power supplynode receiving power supply voltage Vcc1 and a power supply switchcircuit SW4 provided between virtual ground line GNDV and a ground node.

Power supply switch circuit SW3 is constructed of an n channel MIStransistor NQ1 connected between a power supply node receiving powersupply voltage Vcc1 and virtual power supply line VCCV, and having itsgate receiving switch control signal φ and its backgate connected to aground node. N channel MIS transistor NQ1 has a gate insulation film ofthickness Tox2.

Power supply switch circuit SW4 is constructed of a p channel MIStransistor PQ1 connected between virtual ground line GNDV and a groundnode, and having its gate receiving a complementary switch controlsignal /φ from CMOS inverter CTL and its backgate connected to a powersupply node supplying power supply voltage Vcc2. P channel MIStransistor PQ1 has a gate insulation film of thickness Tox2.

In the semiconductor device shown in FIG. 8, an MIS transistor having agate insulation film of thickness Tox1 has a threshold voltage Vth1 inabsolute value set, for example, to 0.2V. An MIS transistor having agate insulation film of thickness Tox2 has a threshold voltage Vth2 inabsolute value set, for example, to 0.5V. Power supply voltage Vcc1 is1.0V and power supply Vcc2 is 2.5V.

The other configuration of the semiconductor device shown in FIG. 8 isthe same to the configuration of the semiconductor device shown inFIG. 1. Accordingly, like components are denoted by like referencecharacters and their detailed description will not be repeated.

In the standby cycle, switch control signal φ is at the ground voltageGND level, as described with reference to the semiconductor device shownin FIG. 1. In this state, CMOS inverter CTL outputs switch controlsignal /φ at the level of power supply voltage Vcc2. Therefore, in powersupply switch circuit SW1, MIS transistor PQ is in a deep off state. Inpower supply switch circuit SW3 also, MIS transistor NQ1 enters an offstate in response to switch control signal φ. MIS transistor NQ1 has agate insulation film of thickness Tox2 and a threshold voltage inabsolute value Vth2 of 0.5V, and an off leak current is sufficiently besuppressed.

Furthermore, in power supply switch circuits SW2 and SW4 also, MIStransistors NQ and PQ1 are both in the off state. They have a thresholdvoltage in absolute value Vth2 of 0.5V, and sufficiently suppress theoff-leak current even in state of a gate to source voltage of 0 V.

When an active cycle starts, switch control signal φ rises to the levelof power supply voltage Vcc2 and CMOS inverter CTL outputs switchcontrol signal /φ falling to the ground voltage level. In this state, inpower supply switch circuits SW1 and SW3, MIS transistors PQ and NQ1both turn on. MIS transistor PQ has a gate to source voltage of +1.0V,whereas in power supply switch circuit SW3, MIS transistor NQ1 has agate to source voltage of 1.5V. Therefore, the on-resistance of MIStransistor NQ1 can be made lower than that of MIS transistor PQ and inthe active cycle, virtual power supply line VCCV can reliably bereinforced to be fixed at power supply voltage Vcc1 and power supplynoise can be suppressed.

For virtual ground line GNDV also, in power supply switch circuit SW2,MIS transistor NQ has a gate to source voltage of 2.5V and virtualground line GNDV is reliably fixed at the ground voltage level. In thiscase, in power supply switch circuit SW4, MIS transistor PQ1 receives,at its gate, ground voltage GND and clamps the voltage level of virtualground line GNDV to the level of absolute value Vth2 of the thresholdvalue thereof, i.e., 0.5V. When the voltage level of virtual ground lineGNDV exceeds absolute value Vth2 of the threshold value of MIStransistor PQ1, MIS transistor PQ1 turns conductive to discharge virtualground line GNDV to the ground voltage GND level, to prevent generationof a large noise on virtual ground line GND.

Note that switch control signal φ may be a signal changing between powersupply voltage Vcc2 and negative voltage VBB. In this case, CMOSinverter CTL is supplied with negative voltage VBB as a low-side powersource voltage. An off-leak current of a power source line in thestandby state can further be reduced and a virtual power source line inan active cycle can further be reinforced.

Modification

FIG. 9 shows a configuration of a modification of the second embodiment.In FIG. 9, to virtual power supply line VCCV, power supply switchcircuit SW3 is provided, and to virtual ground line GNDV, power supplyswitch circuit SW2 is provided. In FIG. 9, power supply switch circuitsSW1 and SW4 shown in FIG. 8 are not provided. Accordingly, there is notprovided CMOS inverter CTL inverting switch control signal φ. The otherconfiguration of the semiconductor device shown in FIG. 9 is identicalto the configuration of the semiconductor device shown in FIG. 8.Accordingly, corresponding components are denoted by like referencecharacters and their detailed description will not be repeated.

In the semiconductor device shown in FIG. 9, in the standby cycle,switch control signal φ is at the ground voltage level and in powersupply switch circuit SW2, MIS transistor NQ is in the off state. Inpower supply switch circuit SW3, MIS transistor NQ1, having a gate tosource voltage of −1.0V (Vcc1 is 1.0V), enters a deep off state, greatlyisolates virtual power supply line VCCV from the power supply node, andsuppresses a leak current in the standby cycle.

In an active cycle, switch control signal φ increases to the level ofpower supply voltage Vcc2 (2.5V). If p channel MIS transistor is solelyused in a power supply switch circuit, then its gate to source voltageattains −1.0V in the active cycle. Where the threshold voltage inabsolute value Vth2 is 0.5V, driving current by p channel MIS transistorin this power supply switch circuit may be inadequate. However, by usingn channel MIS transistor NQ1 in power supply switch circuit SW3, inpower supply switch circuit SW3, MIS transistor NQ1 has a gate to sourcevoltage being 1.5V. If a threshold voltage Vth2 is 0.5V, MIS transistorNQ1 can still transmit power supply voltage Vcc1 of 1.0V to virtualpower supply line VCCV sufficiently with a larger current drive ability.

Furthermore, where an n channel MIS transistor, which is high in chargemobility, is used, virtual power supply line VCCV can be supplied withstable power supply voltage Vcc1 with a smaller occupied area than whena p channel MIS transistor is used as a switching transistor in thepower supply circuit.

Furthermore, it is not necessary to generate complementary switchcontrol signals for power supply control, and accordingly, a circuit forpower supply control can have a reduced layout area.

Furthermore, in power supply switch circuit SW2 also, MIS transistor NQhas a gate to source voltage of 2.5V (=Vcc2), and virtual ground lineGNDV is accurately held at the ground voltage GND level. Accordingly,virtual power supply line VCCV and virtual ground line GNDV can bereliably fixed at prescribed voltage levels and inverters IV1 to IV4 canbe operated stably.

If switch control signal φ changes between negative voltage VBB andpower supply voltage Vcc2, a p channel MIS transistor may be used forhigh and low side power supply switch circuits. In the standby state, anoff leak current can be reduced and a power supply can be stabilized inthe active cycle.

In addition, power supply voltages Vcc1 and Vcc2 may be appliedexternally or internally generated, as described in the firstembodiment.

As described so far, according to the second embodiment, in a powersupply switch circuit, there is arranged an n channel MIS transistorhaving its gate receiving a control signal having an amplitude largerthan a power supply voltage of a logic circuit. Thus, the power supplyvoltage can be supplied stably to a virtual power supply line in anactive cycle and a logic circuit can operate stably.

Third Embodiment

FIG. 10 shows a configuration of the semiconductor device according tothe present invention in a third embodiment. The semiconductor deviceshown in FIG. 10 differs in configuration from the semiconductor deviceshown in FIG. 1 in the following points. The amount of dopant doped intothe channel of a p channel MIS transistor PQ31 constructing power supplyswitch circuit SW1 is made equal to that of dopant into the channel of ap channel MIS transistor PT of CMOS inverters IV to IV4. MIS transistorsPQ31 and PT have their respective gate insulation films of the thicknessthe same as described in the first embodiment, i.e., Tox2 and Tox1,respectively.

In addition, the amount of dopant doped into the channel of an n channelMIS transistor NQ31 constructing power supply switch circuit SW2 isequal to the amount of dopant doped into the channel of an n channel MIStransistor NT of CMOS inverters IV1 to IV4. MIS transistors NT and NQ31have their respective gate insulation films of the thickness the same asdescribed in the first embodiment, i.e., Tox1 and Tox2, respectively.The other configuration of the semiconductor device shown in FIG. 10 isthe same as the configuration of the semiconductor device shown inFIG. 1. Accordingly, corresponding components are denoted by likereference characters and their detailed description will not berepeated.

The MIS transistor has its threshold voltage adjusted by dopingimpurities into its channel region. If an amount of impurities dopedinto an impurity region, i.e., an amount of dopant doped into a channelis the same, a gate insulation film of a larger thickness accompanies athreshold voltage of a larger absolute value. Therefore, the absolutevalue Vth2 of the threshold voltage of p channel MIS transistor PQ31 isgreater than the absolute value Vth1 of the threshold voltage of pchannel MIS transistor PT and the threshold voltage of n channel MIStransistor NQ31 becomes higher than that of n channel MIS transistor NT.MIS transistors PQ31 and NQ31 have a threshold voltage in absolute valueof, for example, 0.5V and MIS transistors PT and NT have a thresholdvoltage in absolute value of, example, 0.2V.

In power supply switch circuits SW1 and SW2, MIS transistors PQ31 andNQ31 has an increased absolute value of threshold voltage, so that asubthreshold current in an off state can be reduced and a leak currentin a standby state can further be reduced. By simply applying aso-called “dual gate insulation film process” in producing MIStransistors with gate insulation films of two kinds of thickness Tox1and Tox2, a threshold voltage of MIS transistor for the power supplyswitching can be made different from the threshold voltage of MIStransistor for the logic circuit. Here, the “dual gate insulation filmprocess” refers to the process of forming a gate insulation film of thesame thickness and then using a mask to selectively form a thick gateinsulation film to produce gate insulation films of two kinds ofthickness.

As described so far, the amount of the impurity into the channel regionof an MIS transistor in a power supply switch circuit is made equal tothat of impurity into the channel region of an MIS transistor (PT, NT)of the same conductivity in the logic gate circuit and the thickness ofthe gate insulation film of the MIS transistor of the power supplyswitch circuit is greater than that of the gate insulation film of theMIS transistor of the logic gate circuit. Thus, the MIS transistor ofthe power supply switch circuit can readily have a threshold voltagelarger in absolute value than the MIS transistor of the logic gatecircuit and a leak current (a subthreshold current and a gate tunnelcurrent) in a standby state can be reduced without complicating afabrication process.

First Modification

FIG. 11 shows a configuration of the semiconductor device of a firstmodification in the third embodiment. The semiconductor device shown inFIG. 11 is different from the semiconductor device shown in FIG. 1 inthe following points. In power supply switch circuit SW1, a p channelMIS transistor PQ22 has a channel length Lp2 made longer than an maximalvalue Lp1 (max) of a channel length Lp1 of p channel MIS transistors PTincluded in CMOS inverters IV1 to IV4.

In addition, in power supply switch circuit SW2, an n channel MIStransistor NQ32 has a channel length Ln2 made longer than a maximalvalue Ln1 (max) of a channel length Ln1 of n channel MIS transistors NT1in CMOS inverters IV1 to IV4.

The other configuration of the semiconductor device shown in FIG. 11 isthe same as the configuration of the semiconductor device shown inFIG. 1. Therefore, corresponding components are denoted by likereference characters and their detailed description will not berepeated.

In an MIS transistor, a threshold voltage is defined as a gate to sourcevoltage supplying a drain current of a prescribed magnitude under thecondition of application of a prescribed drain voltage. If a channellength is increased, a current supplying ability of an MIS transistor isreduced and accordingly the threshold voltage of the MIS transistor isincreased in absolute value. More specifically, when the channel lengthsof MIS transistors PQ32 and NQ32 are made longer than maximal channellengths LP1 (max) and LN1 (max) of MIS transistors PT and NT of CMOSinverters IV1 to IV4, these power supply switching MIS transistors PQ32and NQ32 have threshold voltages in absolute value larger than those ofMIS transistors PT and NT of the logic circuit.

If the threshold voltage is increased in absolute value, a leak currentin the off state, i.e., a subthreshold current can be reduced.Accordingly, by simply changing a channel length, such off leak currentof power supply switch circuits SW1 and SW2 can be reduced withoutcomplicating fabrication process, and accordingly a leak current (a gatetunnel current and a subthreshold current) of the logic circuit can bereduced and a current consumed in the standby state can be reduced.

Second Modification

FIG. 12 shows a configuration of a second modification of the thirdembodiment. The semiconductor device shown in FIG. 12 is different inconfiguration from the semiconductor device shown in FIG. 1 in thefollowing points. In power supply switch circuit SW1, the amount ofdopant doped into the channel region of p channel MIS transistor PQ33 ismade different from that of dopant doped into the channel region of pchannel MIS transistor PT included in CMOS inverters IV1 to IV4. In thiscase, absolute value Vth2 of the threshold voltage of MIS transistorPQ33 is increased to be greater than absolute value Vth1 of thethreshold voltage of MIS transistor PT.

In power supply switch circuit SW2, the amount of dopant doped into thechannel region of n channel MIS transistor NQ33 is made different fromthat of dopant doped into the channel of n channel MIS transistor NT ofCMOS inverters IV1 to IV4. In this case also, the threshold voltage Vth2of n channel MIS transistor NQ33 is made larger than threshold voltageVth1 of n channel MIS transistor NT.

Absolute value Vth1 of the threshold voltage is, for example, 0.2V andabsolute value Vth2 of the threshold voltage is, for example, 0.5V.

In changing the channel dope amount, for p channel MIS transistors PQ33and PT, when phosphorus (P) or any other n type impurity is doped intoan n type substrate region, the amount of dopant doped into the channelof p channel MIS transistor PQ33 is made larger than that into thechannel of MIS transistor PT. If boron (B) or any other p type dopant isdoped into an n type substrate region of p channel MIS transistors PQ33and PT, the channel dope amount for MIS transistor PQ33 is made smallerthan that for p type MIS transistor PT. Thus, absolute value Vth2 of thethreshold voltage of MIS transistor PQ33 can be set higher than absolutevalue Vth1 of the threshold value of MIS transistor PT.

As for n channel MIS transistors NQ33 and NT also, if a p type substrateregion is subject to channel-doping with an n type impurity, the amountof dopant doped into the channel region of n channel MIS transistor NQ33is made smaller than that into the channel region of MIS transistor NT.If a p type impurity is doped into the p type substrate region to adjusta threshold voltage, the amount of dopant doped into the channel regionof MIS transistor NQ33 is made larger than that of dopant doped into thechannel region of MIS transistor NT. Thus, the absolute value Vth2 ofthe threshold voltage of n channel MIS transistor NQ33 is made greaterthan the absolute value Vth1 of threshold voltage of MIS transistor NT.

In this case, the channel doping amount is adjusted to make greater theabsolute value of the threshold voltage of MIS transistors PQ33 andNQ33, so that an off leak current of MIS transistors P033 and NQ33 inthe standby state can be reduced to reduce a current consumed in thestandby state.

The amounts of dopant doped into the channel regions of MIS transistorsPQ33 and NQ33 in power supply switch circuits SW1 and SW2 are simplymade different from the channel doping amounts for MIS transistors PTand NT in CMOS inverters IV1 to IV4 constructing the logic gate circuit.Without complicating the fabrication process, an off leak current can bereadily reduced in the standby state and accordingly a currentconsumption can be reduced.

In the configuration shown in FIGS. 10 to 12, to power supply switchcircuit SW1 receives switch, control signal /φ is at the ground voltagelevel in the active cycle. If power supply voltage Vcc1 is at a levelhigher than absolute value Vth2 of the threshold voltage of MIStransistors PQ31, PQ32 and PQ33 included in power supply switch circuitSW1, the power supply voltage Vcc1 can be reliably transmitted tovirtual power supply line VCCV.

In power supply switch circuit SW2 also, switch control signal φ is at alevel of the voltage Vcc2 higher than power supply voltage Vcc1. Thecondition Vcc2>Vth2 is met and virtual ground line GNDV is maintainedstably at the ground voltage GND level.

In the third embodiment also, switch control signals φ and /φ each maybe a signal changing between a negative voltage and power supply voltageVcc2.

Furthermore, power supply voltages Vcc1 and Vcc2 may be generated asdescribed in the first embodiment, i.e., may be generated externally orinternally.

As described so far, according to the third embodiment, an MIStransistor constructing the power supply switch circuit and having athick gate insulation film has a threshold voltage adjusted, throughadjustment of channel doping amount or channel length to be greater inabsolute value than that of an MIS transistor constructing the logicgate circuit. Thus, an off leak current in the power supply switchcircuit in the standby state can be reduced and a current consumption inthe standby can be reduced without complicating a fabrication process.

Fourth Embodiment

FIG. 13 shows a configuration of the semiconductor device according to afourth embodiment of the present invention. In this configuration of thesemiconductor device shown in FIG. 13, there is provided a logic gatecircuit 20 receiving the voltages on virtual power supply and groundlines VCCV and GNDV as operating power supply voltages. Logic gatecircuit 20 is constructed of CMOS inverters cascaded in four stages byway of example, as in the first to third embodiments. Their constituentp and n channel MIS transistors each have a gate insulation film ofthickness Tox1.

To virtual power supply and ground lines VCCV and GNDV, power supplyswitch circuits SW1 and SW2 are provided, respectively. Power supplyswitch circuits SW1 and SW2 are constructed of p and n channel MIStransistors each having a gate insulation film of a thickness Tox2,respectively.

Power supply switch circuits SW1 and SW2 have their on/off states set bya power supply control circuit 25 and a CMOS inverter CTL. Power supplycontrol circuit 25 generates switch control signal φ in accordance witha mode instructing signal MOD. CMOS inverter CTL receives and invertsswitch control signal φ from power supply control circuit 25, togenerate a complementary switch control signal /φ. Power supply controlcircuit 25 and CMOS inverter CTL receive power supply voltage Vcc2 as anoperating power supply voltage. When made conductive, power supplyswitch circuits SW1 and SW2 transmit power supply voltage Vcc1 andground voltage to virtual power supply and ground lines VCCV and GNDV,respectively.

Logic gate circuit 20 receives an input signal S of an amplitudecorresponding to the voltage Vcc1.

In this semiconductor device, there are provided an active cycle, astandby cycle and a sleep mode. In the active cycle, the logic gatecircuit 20 performs an operation on the input signal S. In the standbycycle, the logic gate circuit 20 waits for a next operation. In thesleep mode, a processing is halted over a long period of time. In theactive cycle and the standby cycle, a system including the semiconductordevice performs any processing, and the semiconductor device is in anoperable state of performing a logical operational processing.Hereinafter, the active and standby cycles will generically be referredto as a “normal mode.” Power supply control circuit 25 sets a state ofswitch control signal φ in accordance with mode instructing signal MOD.

FIG. 14 is timing chart representing an operation of power supplycontrol circuit 25 shown in FIG. 13. FIG. 14 also represents a state ofinput signal S applied to logic gate circuit 20. Input signal S has itsstate definite in the active cycle and indefinite in the standby cycleand the sleep mode.

In the active cycle, power supply control circuit 25 sets switch controlsignal φ to the level of power supply voltage Vcc2 in accordance withthe mode instructing signal. CMOS inverter CTL outputs complementaryswitch control signal /φ at the ground voltage level. Accordingly, inthe active cycle, virtual power supply and ground lines VCCV and GNDVreceive power supply voltage Vcc1 and the ground voltage, respectively.

In the standby cycle and the sleep mode, power supply control circuit 25sets switch control signal φ to the ground voltage level. In response,switch control signal /φ from CMOS inverter CTL is set to the level ofthe voltage Vcc2. Responsively, power supply switch circuits SW1 and SW2are turned off, and virtual power supply and ground lines VCCV and GNDVare disconnected from power supply and ground nodes, respectively.

In the operation timing chart shown in FIG. 14, only in the active cyclein which logic gate circuit 20 actually operates on input signal S,virtual power supply and ground lines VCCV and GNDV are coupled withpower supply and ground nodes, respectively. In control on the switchcontrol signal as shown in FIG. 14, only in the active cycle, powersupply switch circuits SW1 and SW2 turn into an operative state, tosupply logic gate circuit 20 with an operating current. Therefore,control for power supply control circuit 25 can be facilitated, and anoperating current is supplied to logic gate circuit 20 only for arequired period of time and a current consumption can be reduced.

FIG. 15 schematically shows a configuration of a portion of generatingmode instructing signal MOD and switch control signal φ shown in FIG.13. In FIG. 15, a mode instructing signal generating portion includes acontrol circuit 30 receiving an externally applied control signal EXSIGto generate control signals instructing a variety of modes of operation.

In control circuit 30, there is provided a mode detection circuit 32generating a mode instructing signal instructing a mode of operationdesignated in accordance with external control signal EXSIG. FIG. 15shows an active cycle instructing signal ACT activated when the activecycle is designated and a sleep mode instructing signal SLP activatedwhen the sleep mode is designated, as representative of operation modeinstructing signals generated by mode detection circuit 32.

Power supply control circuit 25 includes a buffer circuit 26 receivingand buffering active cycle instructing signal ACT from mode detectioncircuit 32 as mode instructing signal MOD, to generate switch controlsignal φ.

Active cycle instructing signal ACT is held at the H level while thesemiconductor device is in the active cycle. In response, switch controlsignal φ is at the H level. In the standby cycle, active cycleinstructing signal ACT attains the L level and switch control signal φresponsively attains the L level.

In the semiconductor device in the sleep mode, an internal operationthereof is suspended, active cycle instructing signal ACT is at the Llevel, and switch control signal φ responsively also is set at the Llevel. Sleep mode instructing signal SLP is used to control an operationof a circuit portion not shown. Sleep mode instructing signal SLP may beused, for example, to fix an internal node at a prescribed potential inthe sleep mode or to maintain a specific internal circuit (not shown) ina reset state in the sleep mode.

Mode detection circuit 32 is responsive to external control signal EXSIGfor generating mode instructing signals ACT and SLP. However, where acounter provided internal to the semiconductor device performs acounting operation and the sleep mode is designated in accordance withan output of the counter when no operational processing in performed fora predetermined period of time, mode detection circuit 32 receives asleep mode instructing signal from the timer, in place of the externalcontrol signal.

A signal of a logical sum of an inverted signal of active cycleinstructing signal ACT, i.e., ZACT and sleep mode instructing signal SLPmay be used as switch control signal φ. Complementary active cycleinstructing signal ZACT is set at the H level in the standby cycle. Inthis configuration, even if active cycle instructing signal ACT iserroneously activated in the sleep mode, the power supply switch circuitcan be maintained in the off state.

If the semiconductor device is a dynamic random access memory (DRAM), aself refresh mode is set in the sleep mode and memory cell data arerefreshed in predetermined periods, switch control signal φ for circuitrelated to a refresh operation is activated in the refresh operation. Ina circuit not related to the refresh operation, such as column-relatedcircuit, the power supply switch circuit, in the sleep mode, ismaintained in the off state in response to switch control signal φ. Asactive cycle instructing signal ACT, an array activation signal is usedto generate a switch control signal for a power supply switch circuitarranged for a row-related circuit. Thus, in the self refresh mode inwhich refreshing is effected, a refreshing circuit (the row-relatedcircuit) can stably be supplied with a power supply voltage.

Where control circuit 30 receives power supply voltage Vcc1 as anoperating power supply voltage, power supply control circuit 25 isprovided with a level conversion function of converting, to a signal ofamplitude Vcc2, a signal of amplitude Vcc1 outputted from mode detectioncircuit 32.

In the mode switching of transitioning from the sleep mode to the normalmode, transition to the active cycle is prohibited until elapse of apredetermined period of time after the sleep mode completes. Thispredetermined period of time is determined in accordance with thespecification. Therefore, in transition from the sleep mode to theactive cycle, virtual power supply and ground lines VCCV and GNDV can bedriven sufficiently to prescribed voltage levels.

If the semiconductor device operates at a high frequency, there is acase where the active cycle and the standby cycle is rapidly beswitched. If an MIS transistor having a thick gate insulation film isutilized for the power supply switch circuit, there is a possibilitythat virtual power supply and ground lines VCCV and GNDV cannot bedriven sufficiently to prescribed voltage levels in transition from thestandby cycle to the active cycle in the normal mode. Therefore, theapproach shown in FIG. 14 is effective when the semiconductor deviceoperates at a low frequency.

First Modification

FIG. 16 shows a configuration of the semiconductor device in a firstmodification of the fourth embodiment. The semiconductor device shown inFIG. 16 differs in configuration from the semiconductor device shown inFIG. 13 in the following points. A power supply control circuit 35generating switch control signal φ receives power supply voltage Vcc1 asan operating power supply voltage. Power supply control circuit 35 isresponsive to active cycle instructing signal ACT for generating switchcontrol signal φ changing between the voltage Vcc1 and a ground voltage.Moreover, CMOS inverter CTL generating a complementary switch controlsignal /φ receives, through a power supply select circuit 37, one ofpower supply voltages Vcc1 and Vcc2 as an operating power supplyvoltage. Power supply select circuit 37 is responsive to sleep modeinstructing signal SLP for selecting a power supply voltage. Sleep modeinstructing signal SLP is generated from mode detection circuit 32 shownin FIG. 15, and it has an amplitude Vcc2 and is held in an active statein the sleep mode. Power supply select circuit 37 selects power supplyvoltage Vcc2 when sleep mode instructing signal SLP instructs the sleepmode, and otherwise selects power supply voltage Vcc1.

The other configuration of the semiconductor device shown in FIG. 16 isidentical to the configuration of the semiconductor device shown in FIG.13. Accordingly, corresponding components are denoted by like referencecharacters and their detailed description will not be repeated.

FIG. 17 is timing chart representing an operation of the FIG. 16semiconductor device. With reference to the FIG. 17, the operation thesemiconductor device shown in FIG. 16 will now be described.

The semiconductor device has a normal mode and a sleep mode as its modesof operation. The normal mode has an active cycle in which logic gatecircuit 20 performs an operational processing in accordance with inputsignal S, and a standby cycle in which the logic gate circuit 20 waitsfor a subsequent processing.

When active cycle instructing signal ACT is at the L level (an inactivestate), power supply control circuit 35 sets switch control signal φ tothe ground voltage level. In the normal mode, sleep mode instructingsignal SLP is at an inactive state of the L level and power supplyselect circuit 37 selects power supply voltage Vcc1 and supplies it toCMOS inverter CTL as a power supply voltage. Therefore, during thestandby in the normal mode, switch control signal /φ is the level of thevoltage Vcc1 and power supply switch circuits SW1 and SW2 are in anon-conductive state.

In the active cycle, power supply control circuit 35 is responsive toactive cycle instructing signal ACT for driving switch control signal φto the voltage Vcc1 level. Responsively, power supply switch circuit SW2is rendered conductive and virtual ground line GNDV is maintained at theground voltage level. CMOS inverter CTL outputs complementary switchcontrol signal /φ at the ground voltage level, power supply switchcircuit SW1 turns conductive, and virtual power supply line VCCVreceives power supply voltage Vcc1.

In the sleep mode, active cycle instructing signal ACT is at the L leveland power supply control circuit 35 sets switch control signal φ to theground voltage level. Sleep mode instructing signal SLP is at the Hlevel in the sleep mode, and power supply select circuit 37 selectspower supply voltage Vcc2. CMOS inverter CTL receives the power supplyvoltage Vcc2 as an operating power supply voltage. Switch control signalφ is at the ground voltage level and complementary switch control signal/φ accordingly attains the level of power supply voltage Vcc2. Thus,power supply switch circuit SW1, in the sleep mode, enters a deeper offstate, an off leak current in power supply switch circuit SW1 isreduced, and accordingly, an off leak current and gate tunnel current inlogic gate circuit 20 is reduced.

Switch control signals φ and /φ have different amplitudes in the sleepmode. However, switch control signal φ is at the H level in the sleepmode and in CMOS inverter CTL, the p and n channel MIS transistors turnon and off, respectively. Therefore, CMOS inverter CTL is notparticularly required to have a level conversion function. Sleep modeinstructing signal SLP is a signal of amplitude Vcc2, and therefore, itis merely required to perform switching between power supply voltagesVcc1 and Vcc2 in power supply circuit 37.

Power supply select circuit 37 utilizes, as a component, an MIStransistor having a gate insulation film of thickness Tox2. With a CMOStransmission gate, power supply voltages Vcc1 and Vcc2 can betransmitted without a loss by a threshold voltage of the MIS transistor.

In the normal mode, switch control signals φ and /φ have an amplitude ofVcc1 and can rapidly change their voltage levels to switch the on/offstates of power supply switch circuits SW1 and SW2 between the activecycle and the standby cycle. Therefore, even if the semiconductor deviceoperates at high speed and the active and standby cycles are switched athigh speed, virtual power supply and ground lines VCCV and GNDV can beset stably to prescribed voltage levels, respectively, and fastoperation can be ensured.

In the standby cycle, MIS transistors in power supply switch circuitsSW1 and SW2 simply have their source and gate voltages set to the samevoltage level, and a gate leak current is slightly increased. However,by maintaining power supply switch circuit SW1 in the sleep mode to adeep off state and reducing the off leak current therein, a required lowcurrent consumption can adequately be achieved. In high speed operation,the duty of the standby cycle in the normal mode is small, and a currentconsumed in the standby cycle can be made sufficiently smaller inpractical use, as compared with a current consumed in the active cycle.In particular, low power consumption performance is required by portableequipment and others in a data holding mode. By reducing a currentconsumed in the sleep mode, low power consumption feature required inpractical use can adequately be met.

Second Modification

FIG. 18 shows a configuration of a second modification of the fourthembodiment. The semiconductor device shown in FIG. 18 differs inconfiguration from the semiconductor device shown in FIG. 13 in thefollowing points. A power supply control circuit 40 is responsive tosleep mode instructing signal SLP to generate switch control signal φ.Power supply control circuit 40 receives power supply voltage Vcc2 as anoperating power supply voltage, and accordingly, switch control signal φhas an amplitude of Vcc2 as in the arrangement shown in FIG. 13. Theother configuration of the semiconductor device shown in FIG. 18 is thesame as the configuration of the semiconductor device shown in FIG. 13.Accordingly, corresponding components are denoted by like referencecharacters and their detailed description will not be repeated.

FIG. 19 is timing chart representing an operation of the semiconductordevice shown in FIG. 18. With reference to FIG. 19, the operation of thesemiconductor device shown in FIG. 18 will now be described.

Power supply control circuit 40 sets switch control signal φ to thelevel of voltage Vcc2 in the normal mode with sleep mode instructingsignal being at an inactive state. Accordingly, CMOS inverter CTLoutputs complementary switch control signal /φ at the ground voltagelevel. Responsively, power supply switch circuits SW1 and SW2 turnconductive to supply the virtual power supply and ground lines VCCV andGNDV with power supply voltage Vcc1 and the ground voltage,respectively.

Thus, in the normal mode, during both the active cycle and the standbycycle, power supply control circuit 40 sets switch control signal φ tothe level of power supply voltage Vcc2 and sets power supply switchcircuits SW1 and SW2 to a conductive state. Therefore, even if thesemiconductor device is operated at a high frequency and the activecycle and the standby cycle are switched at high speed, the connectionstate between virtual power supply and ground lines VCCV and GNDV andpower supply and ground nodes are invariant, so that logic circuit 20can be operated at high speed.

In the sleep mode, power supply control circuit 40 is responsive tosleep mode instructing signal SLP to set switch control signal c to theground voltage level. Responsively, CMOS inverter CTL outputscomplementary switch control signal /φ at the level of power supplyvoltage Vcc2. Accordingly, power supply switch circuit SW1 enters a deepoff state and its off leak current can reliably be reduced.Correspondingly, a gate tunnel leak current and an off leak current inlogic gate circuit 20 can be reduced.

Thus, power consumption in the sleep mode can be reduced, with highspeed operation feature maintained.

FIG. 20 shows an exemplary configuration of power supply control circuit40 shown in FIG. 18. In FIG. 20, power supply control circuit 40includes an inversion circuit 41 receiving sleep mode instructing signalSLP and having a level conversion function. Inversion circuit 41 withthe level conversion function converts the sleep mode instructing signalSLP of amplitude Vcc1 into switch control signal of amplitude Vcc2.Sleep mode instructing signal SLP is applied from mode detection circuit32 shown in FIG. 15. If sleep mode instructing signal SLP is externally,directly applied and set to the level of voltage Vcc2 when activated,inversion circuit 41 is not particularly required to have a levelconversion function.

When this semiconductor device is a dynamic random access memory (DRAM),an active cycle, a standby cycle and a sleep mode correspond to anactive cycle, a standby cycle and a self refresh mode, respectively.Therefore, a power down mode to suspend power supply to the circuitrynot related to data retention operation in DRAM may be set in the sleepmode. In this case, the semiconductor device in the fourth embodimentcorresponds to a portion of a circuit related to data retention.

If logic gate circuit 20 is a circuit related to selection of a row andrelated to data retention in a DRAM, when a memory cell data isrefreshed, switch control signal φ needs to be set to the H level. Aself refresh mode does not require fast operation. Therefore, whenswitch control signal φ of the level of power supply voltage Vcc2 ischanged to the ground voltage level, a sufficient temporal margin can betaken, and virtual power supply and ground lines VCCV and GNDV can beset to their predetermined voltage levels. To a power supply controlcircuit of a row-related circuit, a control signal corresponding to acombination of sleep mode instructing signal SLP and refresh enablesignal instructing refreshing execution is applied.

As described so far, according to the fourth embodiment, a power supplyswitch control signals of a plurality of amplitudes are prepared and inresponse to the state of the operation, the amplitude of switch controlsignals is switched. Thus, current consumption in an operation requiringlow current consumption feature can be reduced reliably whilemaintaining high speed operation feature.

Fifth Embodiment

FIG. 21 schematically shows a general configuration of the semiconductordevice according to a fifth embodiment of the present invention. In FIG.21, the semiconductor device includes a plurality of circuit blocks LCK1to LCKn. Circuit blocks LCK1 to LCKn may be functional blocks performingdifferent functions, respectively. Furthermore, if a memory array isdivided in a plurality of array blocks as in a semiconductor memorydevice, the circuit block may be a peripheral circuit block providedcorresponding to each array block. The peripheral circuit block includesa row decoder and a local control circuit.

For circuit blocks LCK1 to LCKn, high-level side power source switchcircuits SW11-SWn1 are provided, respectively, and low-level side powersource switch circuits SW12 to SWn2 are provided, respectively. Powersupply switch circuits SW11 . . . SWn1 and SW12 . . . SWn2 are eachconstructed of p and n channel MIS transistors each having a gateinsulation film of thickness Tox2. Circuit blocks LCK1 to LCKn are eachcomprised of an MIS transistor having a gate insulation film ofthickness Tox1.

For power supply switch circuits SW11 to SWn1, CMOS inverters LCTL1 toLCTLn are provided for generating switch control signal /φ1 to /φn,respectively. CMOS inverters LCTL1 to LCTLn receive switch controlsignals φ1 to φn, respectively, from power supply control circuit 50.

For CMOS inverters LCTL1 to LCTLn, power supply select circuits PVS1 toPVSn are provided, respectively. Power supply select circuits PVS1 toPVSn each select one of power supply voltages Vcc2 and Vcc1 in responseto sleep mode instructing signal SLP. Power supply select circuits PVS1to PVSn select power supply voltage Vcc2 o when sleep mode instructingsignal SLP is active. When sleep mode instructing signal SLP is inactiveto instruct the normal mode, power supply select circuits PVS1 to PVSnselect power supply voltage Vcc1. Power supply switch circuits SW11 toSWn1 are supplied with power supply voltage Vcc1. Power supply voltagesVcc1 and Vcc2 have a relationship identical to that of power supplyvoltages Vcc1 and Vcc2 in the semiconductor devices of the first tofourth embodiments.

Power supply control circuit 50 is responsive to mode instructing signalMOD and a circuit block designation signal BS for setting switch controlsignal φ for a designated circuit block to an active state (the Hlevel). Power supply control circuit 50 receives power supply voltageVcc1 as an operating power supply voltage, and switch control signals φ1to φ n each have an amplitude equal to power supply voltage Vcc1.

FIG. 22 is timing chart representing an operation of the semiconductordevice shown in FIG. 21. With reference to FIG. 22, the operation of thesemiconductor device shown in FIG. 21 will now be described. In FIG. 22,switch control signals φj and /φj for circuit block LCKj arerepresentatively shown, where j=1 to n.

In the normal mode, sleep mode instructing signal SLP is an inactivestate and power supply select circuits PVS1 to PVSn select power supplyvoltage Vcc1 and supply it to their respective CMOS inverters LCTL1 toLCTLn as an operating power supply voltage. In the active cycle, powersupply control circuit 50 is responsive to mode instructing signal MODand circuit block designation signal BS, to drive for a selected circuitblock to an active state and to maintain switch control signal φj for anon-selected circuit block at the L level of inactive state. In FIG. 22,the state of the switch control signal for a selected circuit block isindicated by a solid line, and the state of the switch control signalfor a non-selected circuit block is indicated by a broken line.

When switch control signal φj is driven to a selected state, its voltagelevel is the power supply voltage Vcc1 level. In the standby state,switch control signal φj is at the ground voltage GND level, and CMOSinverter LCTLj outputs switch control signal /φj at the power supplyvoltage Vcc1 level. Therefore, switch control signals φj and /φj in thenormal mode change with a small amplitude of an amplitude Vcc1, and thecorresponding circuit block LCKj is supplied with power supply voltageVcc1 and ground voltage GND rapidly.

Even if circuit blocks LCK1 to LGKn operate at high speed and thestandby cycle and the active cycle are rapidly switched, the virtualpower supply line (VCCV)) and the virtual ground line (GNDV) can bemaintained at a stable voltage level.

In particular, these virtual power supply and ground lines are simplyarranged for a corresponding circuit block, and have a small load.Therefore, the power supply switch circuit, in transition from thestandby cycle to the active cycle, can rapidly drive correspondingvirtual power supply and ground lines to predetermined voltage levels.

Furthermore, an actually operating circuit is supplied with the powersource voltage and a corresponding circuit block alone operates. Anunselected circuit block is not supplied with a current, and a currentconsumption can be reduced.

When a transition is made to the sleep mode, power supply selectcircuits PVS1 to PVSn select, in response to sleep mode instructingsignal SLP, the power supply voltage Vcc2 and supply it to theirrespective CMOS inverters LCTL1 to LCTLn as an operating power supplyvoltage. In this case, power supply control circuit 50 is responsive tothe sleep mode instructing signal (included in mode instructing signalMOD) to maintain all of switch control signals φ1 to φn at the groundvoltage GND level. CMOS inverters LCTL1 to LCTLn generate, without alevel conversion, switch control signal /φ1 to /φn (/φj) of the level ofpower supply voltage Vcc2 to power supply switch circuits SW11 to SWn1,respectively.

In this sleep mode, power supply switch circuits SW11 to SWn1 enter adeep off state and their respective off leak currents are reduced.Responsively, a gate tunnel current and an off leak current at the MIStransistors of thickness Tox1 in circuit blocks LCK1 to LCKn can bereduced.

Thus, where an internal logic gate circuit is divided into circuitblocks LCK1 to LCKn, the load of each virtual power supply line and eachvirtual ground line can be reduced, and in transition to the activecycle, the voltage levels of the virtual power supply and ground linesfor a selected circuit block can be set rapidly by the correspondingpower supply switch circuits SW11 to SWn1 and SW12 to SWn2 topredetermined voltage levels. Furthermore, switch control signal φj hasan amplitude of Vcc1 in the normal mode and its state can rapidly beswitched in response to a mode instructing signal, and accordingly, theentire semiconductor device maintains its operation speed withoutdegradation.

Furthermore, power supply switch circuits SW11 to SWn1 receive switchcontrol signals /φ1 to /φn of voltage Vcc2 level, respectively, and areset to a deep off state in the sleep mode, and the respective off leakcurrents are reduced.

As for the configuration of power supply control circuit 50, such aconstruction would be sufficient that buffer circuit 26 shown in FIG. 15is provided for each of circuit blocks LCK1 to LCKn and when activecycle instructing signal ACT is activated and a corresponding blockdesignation signal BS is also in a selected state, a corresponding oneof switch control signals φ1 to φn are driven to the voltage Vcc1 level.It is sufficient to provide, for each circuit block, a gate circuit fortaking a logical product of active cycle instructing signal ACT andblock designation signal BS (BSj).

Due to the division into circuit blocks LCK1 to LCKn, loads of virtualpower supply lines and virtual ground lines can be reduced. Where acorresponding virtual power supply and ground lines can be driven to apredetermined voltage level sufficiently even if the state of a powersupply switch circuit is switched between the active cycle and thestandby cycle in response to a switch control signal of an amplitude ofVcc2, power supply voltage Vcc2 may be supplied to CMOS inverters LCTL1to LCTLn shown in FIG. 21 and switch control signals φ1 to φn may alsobe generated in the form of a signal of amplitude Vcc2.

As described so far, according to the fifth embodiment, an internalcircuit is divided into a plurality of circuit blocks, and the powerswitch circuit is provided for each circuit block and only for aselected circuit block, a corresponding power supply switch circuit isset to the turn on state. Without degradation of high speed operationperformance, current consumption in a mode of operation required of alow current consumption can be reduced.

Sixth Embodiment

FIG. 23 shows a configuration of the semiconductor device according to asixth embodiment of the present invention. In FIG. 23, the semiconductordevice includes cascaded CMOS inverters IVa to IVk as a logic gatecircuit. CMOS inverters IVa to IVk each include a p channel MIStransistor having a gate insulation film of thickness Tox1 and an nchannel MIS transistor having a gate insulation film of thickness Tox1.

A virtual power supply line VDDV and a virtual ground line GNDV areprovided commonly to CMOS inverters IVa to IVk.

For virtual power supply line VDDV, power supply switch circuits SW1 a,SW1 b and SW1 c are provided and, for virtual ground line GNDV, powersupply switch circuits SW2 a, SW2 b and SW2 c are provided. Power supplyswitch circuits SW to SW are each constructed of a p channel MIStransistor selectively made conductive in response to complementaryswitch control signal /φ. The MIS transistors included in power supplyswitch circuits SW1 a to SW1 c each have a gate insulation film ofthickness Tox2.

Power supply switch circuit SW1 a and SW1 c are arranged at oppositeends of virtual power supply line VDDV and power supply switch circuitSW1 b arranged at a central portion of virtual power supply line VDDV.Voltage distribution on virtual power supply line Vccb can be reduced.

Power supply switch circuits SW2 a to SW2 c are each constructed of an nchannel MIS transistor having a gate insulation film of thickness Tox2and selectively rendered conductive in response to switch control signalφ.

Complementary switch control signal /φ is generated from CMOS inverterCTL receiving switch control signal φ. CMOS inverter CTL receives powersupply voltage Vcc2 as an operating power supply voltage. Switch controlsignal φ has an amplitude of the voltage Vcc2.

The virtual ground line is also provided, at opposite ends, with powersupply switch circuits SW2 a and SW2 c, respectively, and with powersupply switch circuit SW2 b at a central portion of the ends, to preventvoltage distribution on virtual ground line GNDV.

FIG. 24 is timing chart representing an operation of the semiconductordevice shown in FIG. 23. With reference to FIG. 24, the operation of thesemiconductor device shown in FIG. 23 will now be described.

In the active cycle, switch control signal φ is at the level of powersupply voltage Vcc2 and switch control signal /φ is at the level ofground voltage GND. In this state, virtual power supply line VDDV issupplied through power supply switch circuits SW1 a to SW1 c with powersupply voltage Vcc1. Similarly, for virtual ground line GNDV, powersupply switch circuits SW2 to SW2 c turn conductive to couple virtualground line GNDV with ground node.

An effect of interconnection line resistance in virtual power supply andground lines VDDV and GNDV and others can be eliminated, voltagedistribution can be prevented from occurring on virtual power supply andground lines VDDV and GNDV, and CMOS inverters IVb to IVk can operatestably. In addition, a plurality of power supply switch circuits SW1 ato SW1 c are be provided to equivalently increase the current supplyingability, and virtual power supply line VDDV can be supplied with powersupply voltage Vcc1 with a large current driving ability. Furthermore,virtual ground line GNDV is also be provided with power supply switchcircuits SW2 a to SW2 c and virtual ground line GNDV can be dischargedwith a large current driving ability to the ground voltage level.Accordingly, CMOS inverters IVa to IVk can be operated in response toinput signal S rapidly and stably.

In the standby cycle, switch control signal is set to the ground voltageGND level and switch control signal /φ to the level of power supplyvoltage Vcc2. Accordingly, p channel MIS transistors included in powersupply switch circuits SW1 a to SW1 c can be set to a deep off state andan off leak current can reliably be reduced in power supply switchcircuits SW1 a to SW1 c, and responsively, a leak current (an off leakcurrent and a gate tunnel current) in CMOS inverters IVa to IVk can bereduced.

Furthermore, even if the active cycle and the standby cycle are switchedat high frequency, virtual power supply and ground lines VDDV and GNDVare driven by a plurality of power supply switch circuits SW1 a to SW1 cand SW2 a to SW2 c, respectively, and the voltage levels of virtualpower supply and ground lines VCCV and GNDV, in transition to the activecycle, can rapidly be stabilized, and CMOS inverters IVa to IVk canrapidly and stably be operated.

In the sleep mode, as in the standby cycle, switch control signal φ isat the ground voltage GND level and switch control signal /φ is at thelevel of power supply voltage Vcc2. As in the standby cycle, powersupply switch circuits SW1 a to SW1 c for virtual power supply line VDDVcan be set to a deep off state, and an off leak current in the powersupply switch circuits in the sleep mode can be reduced. Accordingly, inCMOS inverters IVa to IVk, a gate tunnel current and an off leak currentcan be reduced and a current consumption can be reduced.

Switch control signal φ and /φ may be generated in a manner as in any ofthe first to fifth embodiments.

As described so far, according to the sixth embodiment, a plurality ofpower supply switch circuits are provided for each of a virtual powersupply line and a virtual ground line provided for a logic gate circuit.Consequently, in the virtual power supply and ground lines, adistribution of power supply and ground voltages, caused by aninterconnection line resistance and others can be prevented.Furthermore, in the active cycle, the virtual power supply and groundlines each can have a voltage level maintained stably, and when acircuit operates, an operating power supply voltage can be suppliedstably and generation of power supply node can be suppressed.Accordingly, an operating margin of a logic gate circuit can bemaintained and the logic gate circuit can operate stably at high speed.

Furthermore, in an operation state required of a low currentconsumption, such as the standby cycle and the sleep mode, a powersupply switch circuit is set into a deep off state. Consequently, an offleak current in a power supply switch circuit can prevented in amode/cycle of operation required of a low current consumption andaccordingly, a gate tunnel current and an off leak current in a logicgate circuit can be reduced.

Meanwhile, switch control signal φ can be generated utilizing a powersupply control circuit configured as shown in FIG. 15.

Seventh Embodiment

FIG. 25 shows a configuration of the semiconductor device according to aseventh embodiment of the present invention. The semiconductor deviceshown in FIG. 25 differs in configuration from the semiconductor deviceshown in FIG. 1 in the following points. A precharge circuit 60 isprovided to precharge virtual power supply line VCCV and virtual groundline GNDV to the level of an intermediate voltage (Vcc1)/2 in thestandby state. Precharge circuit 60 includes n channel MIS transistorsNXV and NXG rendered conductive in response to a standby stateinstructing signal φSTB, to transmit intermediate voltage (Vcc1)/2 tovirtual power supply and ground lines VCCV and GNDV. The otherconfiguration of the semiconductor device shown in FIG. 25 is similar tothe semiconductor device shown in FIG. 1. Accordingly, correspondingcomponents are denoted by like reference characters and their detaileddescription will not be repeated.

Switch control signals φ and /φ are Vcc2 in amplitude, and standby stateinstructing signal φSTB is Vcc1 in amplitude.

FIG. 26 is timing chart representing an operation of the semiconductordevice shown in FIG. 25. With reference to FIG. 26, the operation of thesemiconductor device shown in FIG. 25 will now be described.

In the standby cycle, switch control signal φ is at the ground voltageGND level and complementary switch control signal /φ is at the level ofpower supply voltage Vcc2. Furthermore, standby state instructing signalφSTB is at a level of power supply voltage Vcc1. In this state, powersupply switch circuits SW1 and SW2 are in an off state.

In precharge circuit 60, its internal MIS transistors NXV and NXG are ina conductive state in accordance with standby state instructing signalφSTB, to transmit intermediate voltage (Vcc1)/2 to virtual power supplyand ground lines VCCV and GNDV. Accordingly, in the standby cycle,virtual power supply and ground lines VCCV and GNDV is maintained at thelevel of intermediate voltage (Vcc1)/2.

When the active cycle starts, standby state instructing signal φSTBattains the ground voltage GND level. In precharge circuit 60, MIStransistors NXV and NXG turn off and an operation of precharging virtualpower supply and ground lines VCCV and GNDV to the intermediate voltagelevel is terminated.

Furthermore, switch control signal φ is driven to the level of powersupply voltage Vcc2 and complementary switch control signal /φ to theground voltage GND level. Virtual power supply line VCCV is driven bypower supply switch circuit SW1 to the level of power supply potentialVcc1 and virtual ground line GNDV is driven via power supply switchcircuit SW2 to the ground voltage GND level.

If input signal S to logic gate circuit 20 changes in the active cycle,virtual power supply and ground lines VCCV and GNDV are simply drivenfrom intermediate voltage (Vcc1)/2 to power supply voltage VCC and theground voltage GND level, respectively, and virtual power supply andground lines VCCV and GNDV can have a voltage level made definitesubstantially at a fixed timing. More specifically, if precharge circuit60 is not provided, virtual power supply and ground lines VCCV and GNDVhave their voltage levels determined by the amount of the leak currentin logic gate circuit 20. This leak current depends on a gate insulationfilm thickness of and a threshold voltage of a MIS transistorconstructing logic gate circuit 20. The gate insulation film thicknessand the threshold voltage vary for each semiconductor device within acertain range. Consequently, virtual power supply and ground lines VCCVand GNDV, when the active cycle starts, have their voltage levelsdifferent for each semiconductor device, and a worst case needs to beconsidered in determining a circuit operation margin. Therefore, highspeed operation cannot be ensured.

However, as shown in FIG. 25, when virtual power supply and ground linesVCCD and GNDV are fixed, in the standby state, to a predeterminedvoltage level with precharge circuit 60, virtual power supply and groundlines VCCV and GNDV, when the active cycle starts, have their voltagelevels fixed to the precharged voltage level of intermediate voltage(Vcc1)/2, regardless of the leak current in the logic gate circuit 20.Consequently, in each semiconductor device, virtual power supply andground lines. VCCV and GNDV can have their starting voltage levels fixedwhen the active cycle starts, voltages of virtual power supply andground line VCCV can be made definite at a fixed timing, an operatingmargin can be improved, and high speed operation can be ensured. Inparticular, such a state can be prevented from occurring in a sleep modeor others that a standby state is maintained over a long period of timeand the voltage level of the virtual power supply line VCCV is deviatedsignificantly from the power supply voltage Vcc1 and a long time isrequired to restore to the original power supply voltage level to impedethe high speed operation.

Furthermore, since virtual power supply and ground lines VCCV and GNDVare set to an intermediate voltage level, the gate to source voltage ofan MIS transistor in the on state in logic gate circuit 20 can bereduced in absolute value to reduce the gate tunnel current in the MIStransistor in the on state. Furthermore, an MIS transistor in the offstate can have the gate to source voltage set to deeply reverse-biasedstate, and an off leak current of an MIS transistor in a logic gate canbe reduced.

In precharge circuit 60, gate insulation film of MIS transistors NXV andNXG can be any thickness of Tox1 and Tox2, provided that their substrateregions are isolated from the other elements and their backgates are ina floating state.

Furthermore, even if MIS transistors NXV and NXG each have a thresholdvoltage set to 0.5V, intermediate voltage (Vcc1)/2 can be fullytransmitted provided that power supply voltage Vcc1 is at a level of1.0V and standby state instructing signal φSTB has the H level set at alevel of power supply voltage Vcc2. In this case, even if standby stateinstructing signal φSTB has the H level set at a level of the voltageVcc1, MIS transistors NXG and NXV each have the gate to source voltageset at a level of its threshold voltage, and intermediate voltage(Vcc1)/2 can be transmitted. However, these precharging transistors havetheir gate insulation films set to Tox2 in thickness, to reduce a gatetunnel current.

FIG. 27 shows an exemplary configuration of a power supply controlsignal generating portion for generating switch control signal φ andstandby state instructing signal φSTB shown in FIG. 25. In FIG. 27, thepower supply control signal generation portion includes a buffer circuit65 having a level conversion function of converting an amplitude ofactive cycle instructing signal ACT of amplitude Vcc1 to generate switchcontrol signal φ of amplitude Vcc2, and an inversion circuit 66 forinverting active cycle instructing signal ACT to generate standby stateinstructing signal φSTB. Inversion circuit 66 receives power supplyvoltage Vcc1 as an operating power supply voltage.

Active cycle instructing signal ACT is generated, for example, by themode detection circuit shown in FIG. 15, and is activated when thepresent semiconductor device is set to an operating state. Active cycleinstructing signal ACT is an array activation signal (a row selectinstructing signal) for driving a memory cell array to a selected statein a DRAM and corresponds to a chip enable signal in a static randomaccess memory (SRAM).

The power supply control signal generating portion shown in FIG. 27allows switch control signal φ and standby state instructing signal φSTBdifferent in amplitude from each other to be generated based on thecommon active cycle instructing signal ACT.

In the configuration of the power supply control signal generatingportion shown in FIG. 27, in the sleep mode, active cycle instructingsignal ACT attains an inactive state of the L level, and accordingly,standby state instructing signal φSTB attains an active state of the Hlevel. Consequently, during the sleep mode, virtual power supply andground line VCCD and GNDV are precharged to the level of intermediatevoltage (Vcc1)/2.

However, if virtual power supply and ground lines VDDV and GNDV aresmall in duty of the standby cycle and are sufficiently small in voltagevariation in this semiconductor device, or if upon transition from thestandby cycle to the active cycle in a high speed operation, virtualpower supply and ground lines VCCV and GNDV have a voltage level changenot made fast enough, then precharge circuit 60 shown in FIG. 25 may beconfigured to be activated only in the sleep mode to precharge virtualpower supply and ground lines VDDV and GNDV to the intermediate voltagelevel. In such a case, standby state instructing signal φSTB isgenerated simply in accordance with the sleep mode instructing signal.

As described so far, according to the seventh embodiment, when thesemiconductor device is in an operation suspended state, the virtualpower supply line and the virtual ground line are precharged topredetermined voltage levels. Consequently, when the semiconductordevice is released from operation suspended state, the virtual powersupply and ground lines can have reduced voltage variation, a powersupply voltage and a ground voltage can be set, at a faster timing, to adefinite state, a circuit operating margin can sufficiently be ensured,and a circuit operation can be stabilized.

Furthermore, if this precharge voltage is set to a voltage levelintermediate between the power supply voltage and the ground voltage,gate to source voltage of an MIS transistor in the on state can bereduced, a gate tunnel current can effectively be reduced, andaccordingly, a current consumed in an operation suspended state such asthe standby cycle can be reduced.

The configuration utilizing precharge circuit 60 can be combined withany of the configurations of the first to sixth embodiments.

Eighth Embodiment

FIG. 28 shows a configuration of the semiconductor device according toan eighth embodiment of the present invention. In FIG. 28, thesemiconductor device includes a logic gate circuit 20 including aplurality of cascaded inverters. Logic gate circuit 20 includes an MIStransistor having a gate insulation film of thickness Tox1 and performsa predetermined processing (delay and/or inversion in the presentembodiment) in accordance with input signal S.

For logic gate circuit 20, an internal power supply line INPL and avirtual ground line GNDV are arranged. Internal power supply line INPLis connected commonly to sources of p channel MIS transistors in CMOSinverters included in logic gate circuit 20, and virtual ground lineGNDV is connected commonly to sources of n channel MIS transistors inlogic gate circuit 20.

Virtual ground line GNDV is provided with power supply switch circuitSW2 rendered conductive in response to switch control signal φ. Powersupply switch circuit SW2 is constructed of an n channel MIS transistorhaving a gate insulation film of thickness Tox2. Logic gate circuit 20and power supply switch circuit SW2 are similar in configuration tothose in the first to seventh embodiments.

Internal power supply line INPL is provided with a comparison circuit 75for comparing a voltage on a node 73 and a voltage on internal powersupply line INPL to generate a control signal /φA, an n channel MIStransistor 77 rendered conductive in accordance with control signal /φA,for activating the comparison circuit 75, and a power drive circuit SWAfor supplying a current from a power supply node receiving the powersupply voltage Vcc2 to internal power supply line INPL. Comparisoncircuit 75 and enabling transistor 77 are each comprised of an MIStransistor having a gate insulation film of thickness Tox2. Comparisoncircuit 75 receives power supply voltage Vcc2 as an operating powersupply voltage.

Power supply drive circuit SWA is constructed of a p channel MIStransistor PM having a gate insulation film of thickness Tox2. MIStransistor PM is connected between a power supply node supplying powersupply voltage Vcc2 and internal power supply line INPL and has a gatereceiving power supply drive control signal /φA from comparison circuit75.

Comparison circuit 75 receives a voltage on node 73 at a negative inputand a voltage on internal power supply line INPL at a positive input anddifferentially amplifies the voltage on node 73 and the voltage oninternal power supply line INPL when enabled. Comparison circuit 75 mayoutput the signal /φA changing digitally between power supply voltageVcc2 and ground voltage GND, or may output the signal /φA changing inanalog manner in accordance with a difference between the voltage oninternal power supply line INPL and the voltage on node 73.

To set a voltage level on node 73 in accordance with a mode ofoperation, there are provided an inverter 71 receiving a switch controlsignal φ, a CMOS transmission gate 70 rendered selectively conductive inresponse to switch control signal φ and a signal outputted from inverter71, to transmit a reference voltage Vref to node 73, and an n channelMIS transistor 72 rendered selectively conductive in response to asignal outputted from inverter 71, to maintain node 73 at a groundvoltage level. CMOS transmission gate 70 and inverter 71 are eachconstructed of p and n channel MIS transistors each having a gateinsulation film of thickness Tox2. MIS transistor 72 has a gateinsulation film of thickness Tox2.

Inverter 71 receives power supply voltage Vcc2 as an operating powersupply voltage. Switch control signal φ has an amplitude of Vcc2.However, switch control signal φ may change between power supply voltageVcc2 and a negative voltage.

In the semiconductor device shown in FIG. 28, the MIS transistor havingthe gate insulation film of thickness Tox1 has a threshold voltage of0.2V in absolute value and the MIS transistor having the gate insulationfilm of thickness Tox2 has a threshold voltage of 0.5V in absolutevalue.

Reference voltage Vref is 1.0V and power supply voltage Vcc2 is 2.5V.Thickness Tox1 and Tox2 are, for example, 2 nm and 5.5 nm, respectively.

FIG. 29 is timing chart representing an operation of the FIG. 28semiconductor device. With reference to FIG. 29, the operation of thesemiconductor device shown in FIG. 28 will now be described.

In the standby cycle, switch control signal φ is at the ground voltageGND level. Therefore, CMOS transmission gate 70 is non-conductive, whileMIS transistor 72 is conductive, and node 73 is maintained at the groundvoltage GND level. For comparison circuit 75, enabling transistor 77 isturned off and the output signal /φ A is maintained at the voltage levelof power supply voltage Vcc2. In power supply drive circuit SWA, MIStransistor PM is in a non-conductive state.

Such configuration that comparison circuit 75 outputs, when enablingtransistor 77 is in the off state, a signal of the level of power supplyvoltage Vcc2 can be achieved as follows. Comparison circuit 77 isconstructed of a current mirror type differential amplification circuitwith the current mirror stage coupled with the power supply node.Alternatively, a differential amplification circuit is provided, at anoutput portion thereof, with a p channel transistor rendered conductivein response to switch control signal φ, to pull up the output portion tothe power supply voltage level.

In power supply switch circuit SW2 also, the n channel MIS transistorturns off in response to switch control signal φ, and virtual groundline GNDV is disconnected from the ground node. Internal power supplyline INPL and virtual ground line GNDV are maintained at a voltage levelaccording to a leak current in logic gate circuit 20. In the standbycycle, input signal S can be at any logic level.

When the active cycle starts, switch control signal φ is driven to thelevel of power supply voltage Vcc2. Responsively, the MIS transistor inpower supply switch circuit SW2 turns conductive, virtual ground lineGNDV is coupled with the ground node, and its voltage level ismaintained at ground voltage GND.

CMOS transmission gate 70 is made conductive and MIS transistor 72 isnon-conductive, and node 73 receives reference voltage Vref through CMOStransmission gate 70. Enabling transistor 77 turns conductive andcomparison circuit 75 has its comparison operation enabled, to comparevoltage Vcc1 on internal power supply line INPL and reference voltageVref on node 73 and generates current drive control signal /φA based ona result of comparison. When voltage Vcc1 on internal power supply lineINPL is higher than reference voltage Vref, comparison circuit 75outputs a signal of the H level, MIS transistor PM in current drivecontrol circuit SWA has a conductance reduced, and internal power supplyline INPL is supplied with a reduced amount of current. When voltageVcc1 is lower than reference voltage Vref, comparison circuit 75 outputsa signal of the L level, MIS transistor PM has the conductanceincreased, internal power supply line INPL is supplied with an increasedcurrent, and voltage Vcc1 increases in voltage level.

Comparison circuit 75 outputs signal /φA at a voltage level determinedin accordance with a difference between voltage Vcc1 and referencevoltage Vref, and the voltage on internal power supply line INPL attains1.0V equal to reference voltage Vref when stabilized. Power supply drivecircuit SWA supplies internal power supply line INPL with a current andlogic gate circuit 20 operates stably.

A power supply circuit formed of a feed back loop by MIS transistor PMand comparison circuit 75, is used as an internal voltage-downconversion circuit for down-converting power supply voltage Vcc2 togenerate internal power supply voltage Vcc1. Through the use ofvoltage-down conversion circuit for a circuit driving the virtual powersupply line, internal power supply voltage Vcc1 at a desired, optimalvoltage level can be generated from power supply voltage Vcc2.

In the case of using this internal voltage-down conversion circuit also,the current driving MIS transistor PM has a gate insulation film asthick as Tox2 to prevent generation of a gate tunnel current, and canalso be operated as a leak current cutting transistor for logic gatecircuit 20.

In the eighth embodiment, as in the third embodiment, the MIStransistors in the current switch circuit and logic gate circuit 20 mayhave the threshold voltages adjusted through adjustment of channeldoping amount and/or the gate length appropriately.

The current drive transistors in current switch circuit SWA and SW2 andMIS transistor in the logic gate circuit have their channel regionsdoped with impurities to adjust their threshold voltages. If an amountof the impurity implanted into the impurity region, i.e., a channeldoping amount is the same, thicker a gate insulation film is, larger athreshold voltage is in absolute value. Therefore, p channel MIStransistor PM is greater in absolute value of threshold value than the pchannel MIS transistor of logic gate circuit 20, and the n channel MIStransistor of current switch circuit SW2 becomes higher in thresholdvoltage than that of logic gate circuit 20. These MIS transistors incurrent switch circuits each have a threshold voltage in an absolutevalue, for example, of 0.5V, and p and n channel MIS transistors inlogic gate circuit 20 each have a threshold voltage in absolute value,for example, of 0.2V.

An amount of dopant doped into the channel region of the MIS transistorof the power supply switch circuit is made equal to the channel dopingamount of the MIS transistor (PT, NI) of the same conductivity in thelogic gate circuit, and a gate insulation film of the MIS transistor inthe power supply switch circuit is made thicker than that of the MIStransistor of the logic gate circuit. Therefore, the threshold voltageof the MIS transistor of the power supply switch circuit can readily bemade higher in absolute value than the threshold voltage of the MIStransistor in the logic gate circuit, and a leak current (a subthresholdcurrent and a gate tunnel current) in the standby state can be reducedwithout complicating the fabrication process.

In adjusting a channel length, p channel MIS transistor PM in powersupply switch circuit SWA has its channel length made longer than amaximal value of the channel lengths of p channel MIS transistorsincluded in logic gate circuit 20. Furthermore, the n channel MIStransistor in power supply switch circuit SW2 has its channel lengthmade longer than a maximal value of channel lengths of n channel MIStransistors in logic gate circuit 20. When a threshold voltage isincreased in absolute value, a leak current in an off state, or asubthreshold current, can be reduced. Therefore, simply by changing achannel length, an off leak current in power supply switch circuits SW1and SW2 can be reduced without complicating the fabrication process, andaccordingly a leak current (a gate tunnel current and a subthresholdcurrent) of the logic circuit can be reduced and thus, a currentconsumption in the standby state can be reduced.

As an alternative for adjusting an amount of dopant doped into a channelregion, the channel doping amount of p channel MIS transistor PM inpower supply switch circuit SWA is made different from that of the pchannel MIS transistor included in logic gate circuit. In this case,current driving transistor PM has its threshold voltage set larger inabsolute value than the MIS transistor of logic gate circuit 20. Achannel doping amount of the n channel MIS transistor in power supplyswitch circuit SW2 is made different from that of the n channel MIStransistor in logic gate circuit 20. In this case also, the n channelMIS transistor of power supply switch circuit SW2 has its thresholdvoltage set larger in absolute value than n channel MIS transistor NT oflogic gate circuit 20. The channel doping amount is made differentbetween the MIS transistors in power supply switch circuits SWA and SW2and the p and n channel MIS transistors in logic gate circuit 20 simply.An off leak current and hence a current consumed in the standby statecan be reduced without complicating a fabrication process.

Power supply voltage Vcc2 may be an externally applied power supplyvoltage, or may be a down-converted power supply voltage generated byinternally down-converting an external power supply voltage.

For internal power supply line INPL, an n channel MIS transistor havingits conductance controlled by a signal outputted from a comparisoncircuit performing a comparison operation complementary to that ofcomparison circuit 75 may be provided as a current driving transistor.In other words, p and n channel MIS transistors are provided forinternal power supply line INPL as a current driving transistor, toreinforce a power supply. In such arrangement, an n channel MIStransistor having a gate insulation film of thickness Tox2 can beemployed solely as the current driving transistor.

Furthermore, switch control signal φ may have its logic level switchedbetween the normal mode and the sleep mode or the power down mode(including a deep power down mode), as described in the sixthembodiment, not between the active cycle and the standby cycle.Furthermore, if the semiconductor device is a DRAM, switch controlsignal φ may have its state switched between a normal mode and a selfrefresh mode. If the semiconductor device is a circuit related to dataretention, switch control signal φ is set, when a data holding operation(a refresh operation) is actually performed, to an active state tosupply the virtual power supply and ground lines with a current.

For internal power supply line INPL, power supply voltage Vcc2 isdown-converted to generate internal power supply voltage Vcc1. However,as for virtual ground line GNDV, a comparison circuit for comparing areference voltage and the voltage on virtual ground line GNDV may beprovided for switch circuit SW2. In this case, the virtual ground lineGNDV may have the voltage level set higher than the ground voltage GND,to implement a so-called “boosted ground line”, or such an internalpower supply circuit may be implemented that sets virtual ground lineGNDV at the ground voltage level utilizing a negative voltage VBB.

Furthermore, for internal function circuit 20, a plurality of currentdrive circuits may be arranged as well as and a plurality of currentswitch circuits SW2 s may be arranged. Moreover, internal functioncircuit 20 may be divided into a plurality of circuit blocks, for whichinternal power supply line INPL is divided to be arrangedcorrespondingly.

As described so far, in the eighth embodiment, an operation power supplyline is disconnected from a power supply node while operation issuspended, and in operation, the voltage level of the power supply lineis set based on a comparison between another power supply voltage and areference voltage. The voltage on the power supply line can be morestabilized and the internal function circuit can operate stably.

In the first to eighth embodiments, a configuration of a semiconductordevice is individually described, however, the first to eighthembodiments may individually and separately be applied to asemiconductor device, or may be used in an appropriate combination asdescribed previously.

The present invention is applicable to any semiconductor devices thathave an active cycle of performing a predetermined operationalprocessing on a received signal/data, and a standby state (a standbycycle or a sleep mode or a power down mode) of stopping the processing.

Furthermore, it is not particularly required to arrange the power sourceswitch circuit or the current driving transistor for both virtual powersupply and ground lines. Even with current control on one of virtualpower supply and ground lines, a leak current in the standby state canbe reduced as well, while stabilizing an operating current in the activecycle.

As described above, according to the present invention, for a virtualoperation power source line including a virtual power supply line and avirtual ground line, a transistor having a thick gate insulation film isused and its on/off state is adjusted in accordance with a mode ofoperation to control a connection between the virtual operation powersource line and a corresponding power supply node. Thus, an operatingpower source voltage of an internal function circuit in operation can bestabilized and a leak current in stopping of operation can reliably bereduced. A semiconductor device with reduced current consumption and astable and high speed operation can be implemented.

In particular, even if an MIS transistor in an internal logic gatecircuit has a gate insulation film made as thin as no more than 2 nm,the logic gate circuit can be operated stably while reducing the leakcurrent. Thus, a semiconductor device constructed ofultra-microfabricated transistors and operating stably with a reducedcurrent consumption under a low power supply voltage can be implemented.

Although the present invention has been described and illustrated indetail, it is clearly understood that the same is by way of illustrationand example only and is not to be taken by way of limitation, the spiritand scope of the present invention being limited only by the terms ofthe appended claims.

1. A semiconductor device comprising: a plurality of logic circuits eachconstructed of an insulated gate field effect transistor having a firstgate insulation film and processing a received signal; a plurality ofswitching transistors, arranged corresponding to the respective logiccircuits, each having a second gate insulation film greater in thicknessthan said first gate insulation film and rendered selectively conductiveto electrically couple a first power source node and a power node of acorresponding logic circuit in response to a corresponding switchcontrol signal; and a switch control circuit for setting the switchcontrol signal to a switching transistor arranged for a logic circuitamong said plurality of logic circuits set into operating state to anactive state to turn said switching transistor conductive.
 2. Asemiconductor device comprising: a logic circuit constructed of aninsulated gate field effect transistor having a first gate insulationfilm, and receiving a voltage of an internal power line as an operatingpower supply voltage, for processing a received signal; and a pluralityof switching transistors each having a gate insulation film greater inthickness than said first gate insulation film and responsive to aswitch control signal for selectively turning conductive to electricallyconnect a first power supply node with said internal power line.
 3. Thesemiconductor device according to claim 2, wherein said plurality ofswitching transistors include switching transistors arranged at oppositeends of said internal power line and a switching transistor arranged ata central portion of said internal power line.
 4. A semiconductor devicecomprising: a logic gate constructed of an insulated gate field effecttransistor having a first gate insulation film, receiving a voltage ofan internal power node as an operating power supply voltage to operate,and processing a received signal, said internal power node supplying apower supply voltage of a logically high level; and a power supplyswitch circuit including an n channel transistor connected between saidinternal power node and a first power supply node, having a second gateinsulation film greater in thickness than said first gate insulationfilm, and electrically coupling said first power supply node and saidinternal power node when made conductive.
 5. The semiconductor deviceaccording to claim 4, wherein said power supply switch circuit furtherincludes a p channel insulated gate field effect transistor connectedbetween said internal power node and said first power supply node andrendered conductive in a common phase with said n channel transistor inresponse to said switch control signal, said p channel insulated gatefield effect transistor having a gate insulation film greater inthickness than a gate insulation film of a p channel transistor includedin said logic gate.
 6. A semiconductor device comprising: a logic gateconstructed of an insulated gate field effect transistor having a firstgate insulation film, receiving a voltage of an internal power node asan operating power source voltage to operate, and processing a receivedsignal; and a current drive transistor constructed of an insulated gatefield effect transistor having a second gate insulation film greater inthickness than said first gate insulation film, connected between saidinternal power node and a first power source node, for causing a currentflow between said first power source node and said internal power nodein response to a control signal; and a comparison circuit selectivelyenabled in response to an operation mode instructing signal instructinga mode of operation of said logic gate, and comparing said voltage ofsaid internal power node and a reference voltage to generate saidcontrol signal based on a result of comparison.
 7. The semiconductordevice according to claim 6, wherein said current drive transistor andsaid insulated gate field effect transistor of said logic gate are thesame in conductivity type, and said current drive transistor is greaterin channel doping amount than said insulated gate field effecttransistor of said logic gate.
 8. The semiconductor device according toclaim 6, wherein said current drive transistor and said insulated gatefield effect transistor of said logic gate are identical in conductivitytype, and said current drive transistor is larger in channel length thansaid insulated gate field effect transistor of said logic gate.
 9. Thesemiconductor device according to claim 6, wherein said first gateinsulation film is no more than 2.5 nm in thickness and said second gateinsulation film is no less than 3 nm in thickness.
 10. The semiconductordevice according to claim 6, wherein said comparison circuit generatessaid control signal so as to set said current drive transistor into anoff state when disabled.
 11. A semiconductor device comprising: at leastone logic circuit constructed of an insulated gate field effecttransistor having a first gate insulation film, receiving a voltage ofan internal power node as an operating power supply voltage to operate,for processing a received signal of a first amplitude; a switchingtransistor connected between said internal power node and a first powersource node, having a gate insulation film greater in thickness thansaid first gate insulation film, having a threshold voltage no less inabsolute value than a threshold voltage of said insulated gate fieldeffect transistor of said logic gate, for causing a current flow betweensaid first power source node and said internal power node in response toa switch control signal of an amplitude no less than said firstamplitude; and a comparison circuit arranged corresponding to said atleast one logic circuit, selectively enabled in response to an operationmode instructing signal instructing a mode of operation of acorresponding logic circuit and comparing the voltage on said internalpower node and a reference voltage to generate said switch controlsignal in accordance with a result of comparison when enabled.